Point of sale is a large field. You have significant differences between hospitality and retail both in workflow and requirements, for example. Initially I am focusing on retail, which tends to assume fixed locations for cashiers.
Food service is different.... Touchscreens are usually not optional, mobile may be more important (although in retail mobile may be important for niche applications, like taking inventory) and the business requirements are almost nothing like retail. You have all the "configure to order" problems in food service that you don't in retail.
Additionally the same hardware issues are present in food service however, if you want to print a receipt and open a cash drawer, but you *also* have typically shared receipt printers in the kitchen to send orders back. Finally here in Asia while folks do a lot more with cards, the rules are actually more strict, so the card swipe terminal is usually separate (many of these are now 3G however).