Cash workflow:
- Cashier tells you the total amount
- Since I was watching the register display, I already have a rough idea how much this will be, and I have prepared the bills to hand over.
- Cashier gives change and receipt
- I walk away, and after I'm out of the way, I put the change into my wallet.
- Done
Similarly, credit card workflow (American):
- Cashier tells you the total amount
- You insert in chip reader a card you already had out
- You sign, sometimes
- You wait 5 sec for transaction to finish
- You put card back in wallet while receipt is printing
- You put wallet back in trouser pocket while receiving receipt
- Done
The time spent on these is very, very similar. Being prepared with your form of payment and dealing with putting away the results (change, card, receipt) after you leave the line results in a very similar time. Signing (or pin) and waiting on the transaction takes a comparable amount of time to the cashier counting your payment and making change. In each case, less than 15 seconds, and at that point, who cares?