Your price list sets the total
An order’s total is worked out by the system from your own price list, not guessed by the assistant. That one figure is what’s saved, texted to the customer, printed on the ticket and charged. The assistant can’t mark an order as paid, either: an online order only reaches your kitchen once the card payment is confirmed.
Good to knowCard customers see every charge itemised on their payment page before they pay, including a small online service charge.