I've seen some grocery stores with double grocery belts, so the cashier can start checking out the next customer while the first one is finishing payment, they just sweep a divider over so the groceries go down the next belt.

This was well before chip-and-pin, they probably did because of the slowness of writing checks.

Though maybe this is all moot with self-checkout since the store doesn't really care that much if it takes you a bit longer to check out. Especially if they can show you ads while you wait.