@abaker Have you looked at Square? They've made a full-fledged POS application which is very easy to use and manage. They even offer a public web store you can use now.
We're using two Square instances: one for our Cafe, one for our Bookstore.
I'm happy to show you how we're setup and do a screen cast, if you want to see, but I'd honestly look into it. It's easy and simple and the credit card fees are pretty low.