Two ways for making sharing styles with IE

768.css

// just a sample...

div[role="main"] {
  @include un-column;
  @include full;
  @include pie-clearfix;
  @include adjust-font-size-to(21px);
  // we can handle the differences inline...
  .ie7 &, .ie8 & {
    @include trailer(1, 21px); 
  } 
}

susy320.css

@media only screen and (min-width: 768px) {
   @import "768.scss";
}

.ie {
   @import "768.scss";
}