Gruntfile.js

module.exports = function(grunt) {
  require('load-grunt-tasks')(grunt);
  require('grunt-postcss')(grunt);
  
  grunt.initConfig({
    pkg: grunt.file.readJSON('package.json'),
    
    sass: {
      options: {
        sourceMap: false
      },
      dev: {
        options:{
          outputStyle:'expanded'
        },
        files: {
          // Must specify each individual CSS file here
          'css/styles.css' : 'scss/styles.scss'
        }
      },
      dist: {
        options:{
          outputStyle:'compressed'
        },
        files: {
          // Must specify each individual CSS file here
          'css/styles.css' : 'scss/styles.scss'
        }
      }
    },
    
    postcss:{
      options:{
        remove: false,
        map: false,
        processors: [
          require('autoprefixer-core')({
            browsers: ['last 2 versions']
          })
        ]
      },
      dist:{
        src: 'css/*.css'
      }
    },
    watch: {
      options: {
        // Switch to true if using livereload
        livereload: false
      },
      css: {
        files: 'scss/**/*.scss',
        tasks: ['sass:dev', 'postcss:dist']
      }
    }
  });

  grunt.registerTask('default',['watch']);
  grunt.registerTask('build',['sass:dist','postcss:dist']);
}

package.json

{
  "name": "NAME",
  "version": "1.0.0",
  "devDependencies": {
    "autoprefixer-core": "^5.2.0",
    "grunt": "^0.4.5",
    "grunt-contrib-watch": "^0.6.1",
    "grunt-postcss": "^0.5.1",
    "grunt-sass": "^1.0.0",
    "load-grunt-tasks": "^3.2.0"
  }
}