Petty cash tracker

Nothing is stored between visits: closing the tab loses the book, so keep the CSV. The book holds entry order and never re-sorts, does not post to a ledger, and carries one currency at a time, whatever unit you type. The imprest cross-check is the point of the method: after a top-up, the tin holds exactly the float, and the top-up itself equals the vouchers paid out since the last one.