it may help a little, but not that much.
as skoorb mentioned, they'll get the money straight anyways, its not really them financing. Also, if you finance it through their credit department, they actually make more money in the long run
On the other hand, if you have cash in hand, you are a much more serious buyer. It screams, "I WANT TO BUY A CAR NOW I HAVE CASH". And also, they do not have to worry about you being declined for credit and all their time being wasted.