Not sure which bank you deal with but the practice of bringing back half a bill was stopped long ago. At least in Ontario. It used to be as long as the 1 copy of the serial number was intact you would get your money back. Last time I returned half a bill for half it's value was in the late 1980's early 1990's. Perhaps it is in response to the increased ease of counterfeiting a bill/note if you only need to copy the half with the least amount of security.