October Puzzle - Math is for everyone!

The Postmaster is trying to save money by reducing the number of stamps needed to send letters. Postage for an item can be anything from 1 dollar to 15 dollars and you must use exact postage. The new requirement is that you can attach a maximum of three stamps. There are only three different denominations of stamps.  What are they?

On a scale of effortless to diabolical, this rates use your math brain!

Send your answer to puzzle@lansystems.com.  All correct answers will be entered in our monthly drawing.