Missing $1

My friend Sony told me this riddle back in Middle School:

So three monks are traveling home when it starts to rain. Seeing this, they stop by the nearest hotel and check in. The room rate is $30 for one night for all three of them so the monks split the cost three-way and pay $10 each.
The manager later finds out that the three who checked into the hotel are monks and decides to give them a discount. The manager takes $5 and tells the bellboy to go give the monks back some of their money. The bellboy decides to pocket $2 of the $5 and gives $1 to the each of the monks.

So here's the problem:
Technically the monks all paid $9 each for their room. The bellboy pocketed $2 which totals up to $29. What happened to the last dollar?