Jacket + Custom MQ-handling Mixin

_button-group.scss

body {
  margin: 2em;
}

.button {
  background-color: #007dc6;
  border-radius: 0.25em;
  box-sizing: border-box;
  color: #fff;
  display: inline-block;
  line-height: 1;
  padding: 0.6em 1em;
  text-decoration: none;
  transition: opacity 250ms ease-in-out;
  
  &:hover,
  &:focus {
    @include opacity(0.75);
  }
}

.button-group {
  list-style: none none;
  margin: 0;
  padding: 0;
  
  .button {
    display: block;
    text-align: center;
    width: 100%;
    
    &:hover,
    &:focus {
      z-index: 2;
    }
  }
  
  @include respond-to(small) {
    li:not(:first-child) .button {
      border-top-left-radius: 0;
      border-top-right-radius: 0;
    }

    li:not(:last-child) .button {
      border-bottom-left-radius: 0;
      border-bottom-right-radius: 0;
    }
  }
  
  @include respond-to(large, naked) {
    display: table;
    table-layout: fixed;
    width: 100%;
    
    li {
      display: table-cell;
    }
  
    li:not(:first-child) .button {
      border-bottom-left-radius: 0;
      border-top-left-radius: 0;
    }

    li:not(:last-child) .button {
      border-bottom-right-radius: 0;
      border-top-right-radius: 0;
    }
  }
}

_mixins.scss

$breakpoints: (
  'small'  : 'screen and ( max-width:  479px )',
  'large' : 'screen and ( min-width:  480px )'
);

@mixin opacity($amount) {
  $perc: $amount * 100;
  
  -ms-filter: "progid:DXImageTransform.Microsoft.Alpha(Opacity=" + $perc + ")";

  /* IE 5-7 */
  filter: alpha(opacity=$perc);

  /* Netscape */
  -moz-opacity: $amount;

  /* Safari 1.x */
  -khtml-opacity: $amount;

  /* Good browsers */
  opacity: $amount;
}
  
@mixin respond-to($name, $wrap: mq) {
  // If we're inside of a context where there are no media queries
  @include jacket(noqueries) {
    // If $wrap is set to naked, include this content unwrapped no matter 
    // what else the context is
    @if $wrap == naked {
      @content;
    } @else {
      // Include this unwrapped if we are also in the $name context
      @include jacket($name) {
        @content;
      }
    }
  }
  @include jacket(queries) {
    // If we're in a context that does want MQs
    @if map-has-key($breakpoints, $name) {
      // Prints a media query based on the value
      @media #{map-get($breakpoints, $name)} {
        @content;
      }
    }
   
    // If the key doesn't exist in the map
    @else {
      @warn "Unfortunately, no value could be retrieved from `#{$breakpoint}`. "
          + "Please make sure it is defined in `$breakpoints` map.";
    }
  }
}

ie.css

/* line 1, ../sass/_button-group.scss */
body {
  margin: 2em;
}

/* line 5, ../sass/_button-group.scss */
.button {
  background-color: #007dc6;
  border-radius: 0.25em;
  box-sizing: border-box;
  color: #fff;
  display: inline-block;
  line-height: 1;
  padding: 0.6em 1em;
  text-decoration: none;
  transition: opacity 250ms ease-in-out;
}
/* line 16, ../sass/_button-group.scss */
.button:hover, .button:focus {
  -ms-filter: "progid:DXImageTransform.Microsoft.Alpha(Opacity=75)";
  /* IE 5-7 */
  filter: alpha(opacity=75);
  /* Netscape */
  -moz-opacity: 0.75;
  /* Safari 1.x */
  -khtml-opacity: 0.75;
  /* Good browsers */
  opacity: 0.75;
}

/* line 22, ../sass/_button-group.scss */
.button-group {
  list-style: none none;
  margin: 0;
  padding: 0;
  display: table;
  table-layout: fixed;
  width: 100%;
}
/* line 27, ../sass/_button-group.scss */
.button-group .button {
  display: block;
  text-align: center;
  width: 100%;
}
/* line 32, ../sass/_button-group.scss */
.button-group .button:hover, .button-group .button:focus {
  z-index: 2;
}
/* line 55, ../sass/_button-group.scss */
.button-group li {
  display: table-cell;
}
/* line 59, ../sass/_button-group.scss */
.button-group li:not(:first-child) .button {
  border-bottom-left-radius: 0;
  border-top-left-radius: 0;
}
/* line 64, ../sass/_button-group.scss */
.button-group li:not(:last-child) .button {
  border-bottom-right-radius: 0;
  border-top-right-radius: 0;
}

ie.scss

@import 'jacket';
@import 'mixins';

$jacket: noqueries, ie;

@import 'button-group';

screen.css

/* line 1, ../sass/_button-group.scss */
body {
  margin: 2em;
}

/* line 5, ../sass/_button-group.scss */
.button {
  background-color: #007dc6;
  border-radius: 0.25em;
  box-sizing: border-box;
  color: #fff;
  display: inline-block;
  line-height: 1;
  padding: 0.6em 1em;
  text-decoration: none;
  transition: opacity 250ms ease-in-out;
}
/* line 16, ../sass/_button-group.scss */
.button:hover, .button:focus {
  -ms-filter: "progid:DXImageTransform.Microsoft.Alpha(Opacity=75)";
  /* IE 5-7 */
  filter: alpha(opacity=75);
  /* Netscape */
  -moz-opacity: 0.75;
  /* Safari 1.x */
  -khtml-opacity: 0.75;
  /* Good browsers */
  opacity: 0.75;
}

/* line 22, ../sass/_button-group.scss */
.button-group {
  list-style: none none;
  margin: 0;
  padding: 0;
}
/* line 27, ../sass/_button-group.scss */
.button-group .button {
  display: block;
  text-align: center;
  width: 100%;
}
/* line 32, ../sass/_button-group.scss */
.button-group .button:hover, .button-group .button:focus {
  z-index: 2;
}
@media screen and (max-width: 479px) {
  /* line 39, ../sass/_button-group.scss */
  .button-group li:not(:first-child) .button {
    border-top-left-radius: 0;
    border-top-right-radius: 0;
  }
  /* line 44, ../sass/_button-group.scss */
  .button-group li:not(:last-child) .button {
    border-bottom-left-radius: 0;
    border-bottom-right-radius: 0;
  }
}
@media screen and (min-width: 480px) {
  /* line 22, ../sass/_button-group.scss */
  .button-group {
    display: table;
    table-layout: fixed;
    width: 100%;
  }
  /* line 55, ../sass/_button-group.scss */
  .button-group li {
    display: table-cell;
  }
  /* line 59, ../sass/_button-group.scss */
  .button-group li:not(:first-child) .button {
    border-bottom-left-radius: 0;
    border-top-left-radius: 0;
  }
  /* line 64, ../sass/_button-group.scss */
  .button-group li:not(:last-child) .button {
    border-bottom-right-radius: 0;
    border-top-right-radius: 0;
  }
}

screen.scss

@import 'jacket';
@import 'mixins';
$jacket: queries;

@import 'button-group';

The screen.css and ie.css are the output. The gist reordered my files alphabetically :).