The Missing Dollar

Three travelers register at a hotel and are told that their rooms will cost $10 each so they pay $30. Later the clerk realizes that he made a mistake and should have only charged them $25. He gives a bellboy $5 to return to them but the bellboy is dishonest and gives them each only $1, keeping $2 for himself.

So the men actually spent $27 and the bellboy kept $2.What happened to the other dollar of the original $30?

Here it is found! 

Source