最後だけマージンをつけない

HTML

<div class="parent-div">
<div class="div">fii</div>
<div class="div">foo</div>
<div class="div">foo</div>
<div class="div">foo</div>
<div class="div">foo</div>
</div>

CSS

.div{width:100px;height:100;float:left;background:#000;margin-left:10px;color:#fff;}
.noMargin{margin:0 0 0 10px;}

JavaScript

$(document).ready( function() {
    $('.parent-div .div:last').addClass('noMargin')
    });