In most U.S. states (don't know about Texas specifically), hotels are required to post the maximum allowable rate for the room "in a conspicuous place", like the back of the door. The hotel very well could be breaking state law in selling you the room at $5 over-rack.
Fortunately, I don't think I've ever had to pay anywhere near rack--usually closer to about half of whatever's posted. The day I get charged above-rack will be an interesting one.
--Grog--