Billing a fixed cost project in chunks

Billing a fixed cost project in chunks

Hello, I have a fixed cost project that I would like to bill in chunks -- 1/3 when the concept is approved, 1/3 after the first draft and 1/3 when the project is complete. I can create an invoice and where it shows 1 hour, I can replace it with .333333 hours. But it will not give me a nice round number. So for example if my project is $6,600, I would like the first invoice to be $2,200. But instead it comes out to $2,199.98. How can I fix this?