When has it ever been a 5 MPH rule? I have been driving interstates for many many years and gone through speed traps and as long as I am not 10MPH or more over have never been stopped. In fact a NY State trooper (a friend of mine) once told me that that was the "unwritten" rule almost everywhere except maybe Mayberry RFD.
Ever since I can remember. Maybe it's different out east.