Most grocery stores no longer use price tags. They are required to post prices on the shelf. Since all items are barcoded, the systems for checking out assume bar code scans rather than manually inputting of price data at the cash register. Its more reliable to rely on bar codes than a semi-literate clerk.
There was once a time where the store clerks were supposed to remember the prices of all items. It used to be you could ask to see the cow that produced the milk. It used to be you bought chickens live, and took them to be slaughter, and then cleaned them yourself. The world changes.