You should always say thank you.
Luke is checking out at the cash register at a supermarket, and the clerk says have a nice day as he takes his change.
Luke needs to decide whether to respond.
Luke takes the change and smiles at the cashier, thanking them as he walks away.
Luke takes the change from the cashier and walks away without responding.
Luke seems like a pretty ncie guy to the cashier and those around him in the store.
Luke looks like an asshole to the cashier and everyone around him in the store.