what URL do I use to make sure itunes is not blocked?

I am using OPENDNS to block certain sites at home for my kids, and the settings are currently blocking iTunes. I have tried unblocking certain whole categories (movies, television, music, ecommerce/shopping etc are all unblocked) and iTunes is still not accessible. So I am trying to put iTunes on the whitelist, but I can't figure out which URL to write in. I have tried apple.com, itunes.apple.com, itunes.com, etc but none of these seem to be correct. Does anyone have any suggestions. Thanks