Despite popular belief all counter operators at a cash register for a business are sales people and they are very much part of your sales force. Indeed I myself never really realized this until I was 14 years old and working at a McDonalds and they taught us to up-sell customers and we watched a video on how to do this.
For instance they would tell us to ask if the customer would like a Hot Apple Pie or Sunday with that. And you know what to my amazement people would actually say Yes, almost 50% of the time?
Wow, that is incredible indeed. I remember as a young man stopping at Carl's Jr Hamburger after track practice on the way home or to the library to study and they would always ask me if I wanted a carrot or cheese cake with my custom made to order hamburger, I thought that was really stupid, why on Earth would I want a carrot or cheese cake? But sometimes that would prompt me to order a big chocolate chip cookie?
So it worked and while sitting in the dining room I would actually see other people eating guess what? Carrot and Cheese Cake! So, let this be a lesson to you and always manage the sales counter as if they were part of your sales force too, because they are.