Image size for graphics in hover mode

When I create a store in Market Press, it has the graphics in a hover mode, but I can't find the right size of the graphic. So when you look at the products page, like here, you can see the products look blurry, unless you have your mouse right on it. How can I turn that off, so it's just the normal size? Or what size should the graphic be so it doesn't look blurry like that?