Thank You, Not THANKS

My job takes everything pretty seriously. They are very strict on having the customers being treated with the best care as if they are all our bosses. This makes it so there are a lot of rules and regulations based on customer care. The majority of these rules are pretty common, say "hello" and "goodbye" to every customer that walks in, even if they buy nothing, make small talk so the customer doesn't feel awkward, and of course ask if they need help and assist them if they do. One - and this one is a serious one - is something I never heard of until I started working. It is saying "thank you" instead of "thanks" to all of our customers, if we don't we can get in a lot of trouble if we are caught. If we say "thanks" to a secret shopper (people disguised as customers to grade how efficient their cashiers are working) our store leader will be fined $1,000. So yeah, he would probably be pissed if he learned that he got fined due to one of us saying "thanks". I think we could get fired for that. So now every time I hear someone say "thanks" or I say it myself I freak out. I think I am going to get in major trouble until I realize that I am just at school and freaked out for nothing. So my job is definitely improving my speech.