As others have mentioned, one line feeding small cache lines is probably closer to reality, for the reasons that you mention -- buffering so that the cashier is

As others have mentioned, one line feeding small cache lines is probably closer to reality, for the reasons that you mention -- buffering so that the cashier is always occupied. The main goal is to prevent a single "price check" from jamming an entire line of people -- keep the queues at each station as small as possible so that most customers can route around the blockage.