As AbanteCart said, it's that large header image you have. iPad uses Safari as it's browser (unless you're installed a different one) and your style sheet would need to include the fixes for viewing on Safari.
AbanteCart developers worked very had producing this shopping cart, but there are a few issues with different browsers.
You'll need to find a webkit fix for Safari and Chrome 10+ and add it to your style sheet or get rid of that image.