How can I buy something from the vending machine?

Hint 1 of 11:

The machine will only accept correct change.

Hint 2 of 11:

You must deposit all of the money together.

Hint 3 of 11:

Count the change Charles gave you when you paid for your room.

Hint 4 of 11:

You only have $2.50.

Hint 5 of 11:

The least expensive item sells for $2.75.