so he changed the blinds? or he just started raising to $5 with any playable hand. If the BB is $5 and you have a $100 stack then basically take 2 high cards, make a pair on the flop and get it in.

If its only him whos made his blind bigger then its essentially the same as if hes raising with 100% of his hands and folding lots to reraises. That sounds pretty exploitable.