I've never had a problem lying to people I wouldn't see again. Cashiers, customer service people, they're just using the question as a form of greeting. Like when you travel to the land of the Elves and they say, "Let the sunlight shine always on your face" you respond "And always on yours" before conducting business. It's just polite.

Now it's a different thing if a friend asks.

Then it gets more complicated.....