Apologies, you don’t need a -webkit prefixed one as border-radius is supported in Webkit browsers without a vendor prefix.
Validation isn’t the end of the world. You cannot use the latest technologies and have valid CSS because of all the vendor prefixes. If you let that put you off then you might as well give up now!
Try validating the Hardboiled Web Design site, website for one of the forefront books in CSS3 webdesign. It doesn’t validate…Does it matter? Not in the least bit