And most people would be irritated and ring stuff up into the wrong "tab" multiple times a day, because people are bad at multitasking. There is a reason why m

And most people would be irritated and ring stuff up into the wrong "tab" multiple times a day, because people are bad at multitasking. There is a reason why most POS software is intentionally restrictive and violating many common UI imperatives. Many common UI design rules are not governing the case of a user who is specifically trained to use a certain system, but must then use it in stressful situations at maximum speed and minimum error rate.