I would dispute that there's actually any dishonesty going on there. What's missing is the intent to deceive; everybody knows that the greetings are obligatory, and the people saying them may or may not mean them. Consider what would happen if you replaced the greetings with some other arbitrary phrases:
Cashier: Hello. Where is your dog?
Shopper: My dog is on the moon.
Cashier: The gravy orb hovers once again over London.
Shopper: I wish to purchase a kilogram of ground beef.
Cashier: As it is spoken, so let it be.
This conversation has clear falsehoods in it, but nobody expects them to be true, nobody is deceived, and the dishonesty is paper-thin. (Also, writing that dialogue was a lot of fun.)
I once responded to a "hi how are you" with a one-sentence reply of how I actually was rather than the usual "I'm good". It took the guy by surprise to the extent he stopped with a quizzical look and said "you were ready for that, weren't you?". It's possible to greet someone warmly without an empty question being involved.
I know this isn't Reddit, but "The gravy orb hovers once again over London" put such a smile on my face that I'm forced to upvote you for bringing a tiny bit of joy to my day.
Cashier: Hello. Where is your dog?
Shopper: My dog is on the moon.
Cashier: The gravy orb hovers once again over London.
Shopper: I wish to purchase a kilogram of ground beef.
Cashier: As it is spoken, so let it be.
This conversation has clear falsehoods in it, but nobody expects them to be true, nobody is deceived, and the dishonesty is paper-thin. (Also, writing that dialogue was a lot of fun.)