A template to generate a retina/high-res less spritesheet using grunt-spritesmith _without_ using both hi/low res images. Also it generates a bit less bloated rules than default. You might want to modify the template (eg classname and selector) depending on how you prefer to name stuff.

Gruntfile.js

module.exports = function(grunt) {
  // Project configuration.
  grunt.initConfig({
    sprite: {
      icons: {
        src: 'img/icons/*.{png,jpg,gif}',
        destImg: 'img/icons.png',
        destCSS: 'less/general/icons.less',
        algorithm: 'binary-tree',
        cssTemplate: 'path/to/icon.template.mustache'
      }
    }
  });

  // npm tasks
  grunt.loadNpmTasks('grunt-spritesmith');

  // Default task.
  grunt.registerTask('default', ['sprite']);
};

icon.template.mustache

.icon {
  background-image: url({{{items.0.escaped_image}}});
  background-size: {{items.0.px.total_width}}/2 auto;

  {{#items}}
  &.{{name}} {
    background-position: {{px.offset_x}}/2 {{px.offset_y}}/2;
    width: {{px.width}}/2;
    height: {{px.height}}/2;
  }
  {{/items}}
}