With the fiat gateways and wall of coins integration it would seem that already Dash would be better than my local grocery stores POS system in that it could take worldwide currency denominations (for tourist or whatever), or at least the ones we have integrated with through crypto exchanges. Add shapeshift and it could take most all atls too. No?

I'm also not even sure that it would need to be reversible like if the cashier charged me for an extra can of beans. They would just credit my account from the stores account. If it was a larger amount $100-$1000+ she may need to call over her manager who would have access to a multisig store account. And up the chain (non pun intended) of command (3 sigs) it would go if a even larger amount than that was needed to be reversed.
Or maybe that would not scale and it would have to go into masternode purgatory like the current system and all clear later. Either way it can be done with crypto or at least soon with DASH!