The jquery Rounded Corners module is a nice tool if you need rounded corners for divs, classes, blocks etc. I needed rounded corners for a container on my project, I'm using Blueprint 3 framework and this was really easy. The rounded corners module needs to be updated with the latest version, you can download it from here. Replace the version you have in you're Rounded corners module. First I had to create a class for my container:
background-color: #ffffff;
border: 1px solid #cccccc;