Comment by michaelmrose

It's an edge case most hardware doesn't expose the ability to start charging you until the cashier totals it.

The only exception is that with some hardware/software is that within a narrow window it may be possible to go back and make a change after putting the pinpad in payment mode.

Remember the pinpad is a second computer not a peripheral.

I have never in decades of paying for things ever seen a checkout where you can tap right away.