Hi ScrabbleMaster - The official Scrabble rule is to subtract the 'face value' of all tiles on your rack from your total at the end of the game. The face value of a blank is zero, which means no points are deducted.
As for the specific rule, there isn't really one single set of numbered rules, but Hasbro's official site uses the following wording...
---------------------------------------------------- SCRABBLE Rules: Scoring (Selected parts) ---------------------------------------------------- 1. .... The score value of a blank is zero.
9. Unplayed Letters: When the game ends, each player's score is reduced by the sum of his or her unplayed letters. In addition, if a player has used all of his or her letters, the sum of the other players' unplayed letters is added to that player's score.