Or is that impolite? 
When I sneeze, I usually just say 'excuse me' afterwards. If someone wants to bless me, then fine, but I don't much care.
But for some reason my colleague gets arsey when people don't say 'bless you' when she sneezes - to the point that she will passive-aggressively say 'bless me' when she sneezes and shoot pointed glances around the office.
I feel like I'm being rude not blessing her but at the same time it seems a bit daft that anyone would be that bothered!