Genius out there?? Where is my $1???

Could any genius out there please figure this out for me? i'm really so not good with maths

Figure this out:
Three guys in a hotel call room service and order two large pizzas. The delivery boy brings them up with a bill for exactly $30.00. Each guy gives him a $10.00 bill, and he leaves.
That's fact!

When he hands the $30.00 to the cashier, he is told a mistake was made.
The bill was only $25.00, not $30.00. The cashier gives the delivery boy five $1.00 bills and tells him to take it back to the 3 guys who ordered the pizza.
That's fact!

On the way back to their room, the delivery boy has a thought... these guys did not give him a tip. He figures that since there is no way to split $5.00 evenly three ways anyhow, he will keep two dollars forhimself and givethem back three dollars.
OK! So far so good!

He knocks on the door and one fellow answers. He explains about a mix up in the bill, and hands the guy the three dollars, then departs with his two-dollar tip in his pocket.

Now the fun begins!

Remember $30-$25=$5 Right? $5-$3=$2 Right?

So what's the problem?
All is well, right?
Not quite. Answer this:

Each of the three guys originally gave $10.00 each. They each got back $1.00 in change. That means they paid $9.00 each, which times three is $27.00. The delivery boy kept $2.00 for a tip.

$27.00 plus $2.00 equals $29.00.
Where is the other dollar ! ??????????