This sounds very Midwestern to me. Where I come from that would happen a lot. It wasn't necessarily that people didn't know the real name of the place. It functioned more like an inflection that helps to distinguish between the company, and a specific storefront operated by that company. Compare it to the distinction between "Alice" and "Alice's". Alice is the person, and Alice's is her house.

For example, you you'd say "JCPenney stock is up by 32 cents this week," but you'd also say, "I bought this shirt at Penney's."