I ask you to read a sentence in which a $ goes before the amount. Because in most cases, $5 will be read as "five dollars" which makes it more natural to have the $ behind the amount. But then, grammar hates this, so they make it not happen. But then again, this might be a minor OCD for you, thats your problem. Maybe I will buy Magicka for 10$ later though.
EDIT: forget you lolbot.