How to be a good fast food cashier?

Smile, ask "hi how are you?", say "thank you"

Polite

Today’s cash registers make it fairly simple. They are already programmed with the item prices and will tell you everything you need to know about the transaction. What you would need to do is be pleasant to the customers.

Be good at math (add, subtract, multiply, divide).👌
Give back correct amount of change 👌
Don't complain to customer about your job.👌
Follow all orders given to you buy employer. 👌
Practice 5 min a day before opening time.
Make sure you u understand the cash register 👌

be polite, cheery and attentive. I have noticed that employees can be very busy and taking alot of orders and have trouble getting orders right. I might be me taking too softly but repeat the order back if need be.

Be friendly and fast. That's it. Your boss will love you and so will the customers.