"A great many individuals, however, deposited their Dollars in a stronghold called a bank. These banks invested the Dollars in loans and commercial enterprises, with the result that, every time the earth traversed the solar ecliptic, the banks compelled each borrower to repay, or to acknowledge as due, the original loan, plus six one-hundredths of that loan. And to the depositor, the banks paid three one-hundredths of the deposited Dollars for the use of the disks. This was known as three percent, or bank interest."
UPDATE: While this story carries a publication date of 1956, one commentator claims it was actually first published in 1915, when indeed life was more predictable. Good Science Fiction, of course, should be timeless, as this story is.