Using the odd 5 doesn't always do the trick.
Saw a nasty in TC one day. LL Sam departure, Iberia I think.....TURN RIGHT HEADING 245, CONTACT LONDON 124.92...read it back. then went AWOL inbetween freq's climbing to FL245 instead of FL150 and nearly had a nasty with a Navy something or other. Sometimes even belt and braces doesn't do it......