From an autistic perspective, I found 'hi' and the 'how are you?' 'fine' ritual really annoying and meaningless for ages. Then I read about phatic language and social communication, and began to see it as a code. As a way of people acknowledging you, briefly letting you know they are friendly and want to keep you in their life, even though at that particular moment they don't want to engage in a deep conversation. So now I see 'how are you?' 'fine' as a code for mutual friendliness and acknowledgement and keeping someone in your life, rather than a fake, untruthful thing.

I don't like it when cashiers do it though, because they don't know me, and because it's hard to focus on both buying my groceries and participating in small talk. Fortunately in the UK, it's not so common - I found it very uncomfortable when I was in Canada.