Single turnip is ridiculous sure but that is hardly the average sub 5 $ purchase. I have seen people check out with single pieces of fruit or like a gallon of milk regularly. Plus, in my state, you could easily get a single deli item for lunch or breakfast for ~5$ or under. Basket size (which is the term groceries use for the average purchase total) is about 50$ although it has gone up in covid19 times. That is the mean though- there is a ton of ~5$ and sub purchases