Honestly it's not as bad as I thought. I joined as a store associate at a Winners store where I do stocking and being at the cashier, less than two months ago, with no prior job experience as I'm a student. People genuinely don't care who the cashier is so there's not as much pressure. I just say 'how are you doing', 'have a good day', 'good night', etc. in an identical manner to the point where it's like I'm just repeating the same thing and so it's easier. Greet customers with a GENUINE smile and GENUINELY ask how they're doing and after that it becomes much easier to say anything else that would be necessary. You can try to over-announce things like their total amount due; announcing it almost like a ring announcer makes it easier to say as well. With some customers I have a hard and embarrassing time. But as soon the next one comes in, I literally forget about it and move on. My coworkers and managers would probably know atp that I have a speech deficiency but they don't mind it because I don't let it become disastrous.