I think you are going to be hard pressed to find a POS with preloaded inventory and it be accurate for cost and retail pricing. Personally I would rather build from scratch for my business than try to clean up a database of existing items. Either way it is a ton of work. We use Microsoft RMS which is great for multiple locations.
RMS doesn't suck, actually. and we did actually buy a database off another booze merchant in the area when we finally went to scanning (where item descriptors and properties were in place, but the pricing was not); while it did help jump start things, between ALL the items needing to be price changed, ALL the shit that wasn't in prior, and ALL the stupid contractions used as item descriptors, items in the wrong (for us) inventory category, and other "creative differences", it would have been better to use a fresh start.
and, rev, while you do get partial credit (especially when the program acts up!), this is a reference to a Point Of Sale program. o)