No you should be lucky those are the only "bad" social habits you have. If you think trailing off or mumbling is bad, try stuttering on every single word or laughing way too loud like someone who's actually socially awkward.
As a cashier myself, this is so true. I say no problem all the time, and no one else has a problem. You sound just as nice when you say "no problem" vs. "youre welcome" ; Agreed, I say "No problem" to people all the time.