The boyfriends standing there for the whole shift does sound bizarre. Maybe they were chatting with the cashiers the whole time and of course that wouldn’t be okay
Why?
They are human beings, and I want to buy stuff, not get undivided attention.
Well you’re supposed to be at work. To your employer or to customers it might look like you’re distracted and unprofessional, which would reflect badly on the store.
In the small grocery store around the corner where I live the cashier’s are listening to music, having phone calls with their earplugs in or watching videos with their phones lying near the register. The work is boring and repetitive, customer interaction is quite minimal there anyway because they are really fast in ringing you up anyway. And that’s everything I care about anyway. They can enjoy their day a bit more and I can get to doing what I enjoy fast, too.