No one really wants an accurate answer. It's just a greeting. Someone says 'how are you?' you say 'grand' then get on with your day. Same as when someone says 'what's happening?' They don't want a comprehensive list of your woes and such.
Then say something different. Same shit different day, surviving for now, whatever. They'll shrug it off and move on. We all do it. My mom used to say, "it's a good day. I woke up on the right side of the dirt."
Adding a "thanks" acknowledges them asking. "Thanks, how about you?" Doesn't answer the question, but follows the social interaction formula of acknowledgment and throwing it back/mirroring.