Or, in reality, most commodity POS systems are actually able to support various countries and tax regimes, and is plenty ready to be configured a variety of ways and work perfectly fine in changing systems.

For example, the exact same physical hardware in American supermarkets for self checkout is also used in countries like Australia that have more coins than the US, and the machines literally do not have enough coin slots for every coin, so they just don't dispense certain coins in that place.

The POS market is rather robust and has been around the block for quite a while and has no problem managing quite literally arbitrary fees. Businesses in our city added a "cost of living" fee to all bills (just raise prices FFS, so dumb) and they didn't have to go out and buy new POS systems, because POS systems are very configurable.

Like, other industries that have been selling software products for decades are actually kind of good at their jobs and it's really just software as a service that reliably makes garbage. POS software can handle all sorts of things you probably don't even realize.

Go lookup all the functionality that Square advertises their POS systems have, and understand that they are new entrants to the market and do not have all the features that legacy vendors have built up over decades. The functionality has been so thoroughly figured out for so long and so straightforward, that a POS you bought in the 90s is likely still fit for service today.

Meanwhile, retailers are actually open to improving and modernizing their POS infrastructure regularly. They added those coupon printers to existing stacks and didn't have to do anything special because POS systems are absolute legends of interoperability. They use extremely standardized ports, including a special supplementary power version of USB, and are very tolerant to mix and match hardware. POS vendors even sell their hardware without forcing you to buy their software. The system is very open.