decimalAdjust (https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Math/round) that uses increment instead

decimalAdjust.js

function decimalAdjust(type, value, increment) {
  increment = increment || 1;
  
  // If the exp is undefined or zero...
  if (increment === undefined || increment === 1) {
    return Math[type](value);
  }
  value = +value;
  // If the value or increment is not a number...
  if (isNaN(value) || isNaN(increment)) {
    return NaN;
  }
  increment = increment.toExponential().split( "e" );
  // Shift
  value = value.toString().split('e');
  value = Math[type](+(+value[0]/increment[0] + 'e' + (value[1] ? (+value[1] - increment[1]) : -increment[1])));
  // Shift back
  value = value.toString().split('e');
  return +(+value[0]*increment[0] + 'e' + (value[1] ? (+value[1] + increment[1]) : increment[1]));
}