Amazon Interview Puzzles

A man went into a bank with a thousand dollars, all in dollar bills, and ten
bags. He said, “Place this money, please, in the bags in such a way that if I
call and ask for a certain number of dollars you can hand me over one
or more bags, giving me the exact amount called for without opening any of
the bags.”
How was it to be done? We are, of course, only concerned with a single
application, but he may ask for any exact number of dollars from one to one
thousand.