How does Apple achieve the visual "wrap" to form its App store icons on itunes.apple.com?
The trick is to overlay a masking icon which contains a border and some shadow. With CSS this is positioned exactly above the underlying icon.

This is the image: http://r.mzstatic.com/htmlResources/F96C/images/mask175.png

If all you need is rounded corners, there is some CSS (3) only tricks for that, though it will look a bit different then.