Ya it's usually bagged for you, although often enough it's just bagged by the cashier, especially if it's a small amount of food. Depends on the supermarket, but sometimes the bagger drifts lane to lane wherever they're needed.

There are some supermarket chains who are known for cutting costs, where you bag yourself. They usually are different in other ways too, like they don't carry all the same products, or rotate products based on when they can get them cheap etc