ISO a decent, customizable P.O.S. system

I've got a client that would like to have a P.O.S. system for their gift shop, possibly sell items on line, and most importantly, be able to integrate a "Cave Tour." The primary focus of their business is running these cave tours all day long.

A typical sale for them might be: sell a knick-knack, sell 2 adult tickets & 3 child tickets to the tour at 12:30. Keep in mind that the tours run every half-hour, and they only take so many at a time, so traditional inventory management isn't applicable, as each half-hour block will have oh, say 25 openings apiece. They also do group discounts & promotions, which will need to be figured into the bill at the time of purchase. I know they have gotten quotes from many sources, but none of the products that they have looked at seem to be able to accomplish something this sophistocated out of the box.

I know their main goal right now is to reign in on the in-store commerce, with the e-commerce side coming later on. As I deal mainly with web stuff, this is kind of new to me, and I just wanted to know if you guys had had any experience with some of the free/paid P.O.S. systems out there, and if you think that any of them would gel nicely with the client's needs in this case.

I've been looking at http://www.phppointofsale.com - Has anyone worked with this? It looks pretty slick, the price can't be beat, and it seems to have OSCommerce integration, as well as being opensource and therefore completely customizable. Thoughts?

Any suggestions (even to say tuck your tail and run ) would be appreciated!!

Thanks,

VG