Thanks for the feedback. It seems the drag distance threshold was a bit too small, causing clicks and dragging to get mixed up. I've updated the game with that distance tripled, so hopefully clicks should register a bit better now!
I'm working on making customers walk to the cash register on their own. If an employee is present at the register, it should process the customers in line automatically. Most likely you'd have someone standing there at all times. I'll experiment with how that automation feels with employees being stationed at other spots as well!