I’ve noticed that WebKit browsers (only tested Chrome) render borders with round corners differently than in Firefox.
Say you have an image and you give it a 1px solid white border and then set border radius to 5px. Firefox gives you a nice solid 1px wide white line around the image, with round corners. In chrome, however, the white border gets cut off in the corners, and looks awful.
This may or may not fix your problem, but I’ve had several cases where border-radius looked horrible on webkit and this did the trick.
-webkit-background-clip: padding-box;
no guarantee, but worth a shot.
Though overall, the behavior of images and backgrounds in regard to border-radius on most browsers is disastrously bad. You can’t apply it to image at all, it has problems with background-images bleeding past the border radius in webkit…