Found a link to a CSS optimizer web-site CleanCSS via you’ve been HAACKED blog.
A while ago we tried to write PHP script similar to this, but never finished (some urgent stuff always got in our way). Found some tests for that script, ran them through this optimizer – and it works as expected. In fact, it does some thing we never thought of, like removing last semicolon, adding semicolons where needed etc.
This site uses csstidy and there’s even PHP version available for download.