Just had an exchange like this today, and it's basically an everyday occurrence:
Cashier: Hi, how's your day going?
Me: Fine thanks, how are you?
Cashier: Fine, thanks. Did you find everything you were looking for here today?
Me: Yes thanks, except I couldn't find XXX.
Cashier: Oh, sorry - I'll have somebody grab it for you.
Me: Thanks.
(Clerk brings the item)
Me: Sorry - thanks.
Cashier: How would you like to pay?
Me: Debit please.
Cashier: Thanks, go ahead when you're ready.
(Hands me the debit terminal)
Me: Thanks.
Cashier: Would you like the receipt in the bag?
Me: Yes, thanks.
(Passes me the bags)
Cashier: Thanks.
Me: Thanks, good day.
Tons of "thanks", a couple "sorrys" but nobody ever did say "you're welcome".