Apps to keep track of sales for an upcoming event?

I'm on the merchandising committee for an organization and we're having a convention next weekend. I'll be in charge of some merchandise sales and am wondering if there are any good apps to keep track of sales. I don't need anything real fancy, just some basic recording of sales, totals stuff like that. The simpler the better, but something a little better than simply recording as a note in Evernote. I'm looking for iPad or Android apps, but prefer iPad in this case because most my notes and records relating to it are created and stored on my iPad. So, any recommendations? Thanks