Correct - he can't win any more than $5 off you, so you put in $5 and you may as well deal the cards face up.
Technically, you'd put in your $10 big blind then take back the leftover $5, but there's no point in reality.
Where this gets interesting is when you're playing at a full table and the big blind has less than the amount of the big blind in their stack. Then anyone else needs to at least call the amount of the full big blind to play.