Can I use my macbook pro as a surrogate for a cash register? What would I need, would the cost be worth it?

I'm working at a summer camp that has a little trading post, which I'm running and of course the cash registers don't work (no ink, discontinued models). And I was wondering if there was any programs for Apple that I can run on my macbook pro that I can essentially have it be my register. Do the numbers and reports on it, and keep the cash in a cash box. Is there something out there that would do something like this? Something thats not too costly since Id have to purchase it myself and I'm not sure if I'd get reimbursed.