That and it’s not worth it for them. However technically they can get you for going 1mph over speed limit if they wanted an excuse to legally pull you over
The margin here used to be about 5km/h before a police officer would pull one over. No it's as little as 1-2km/h.
Since most speedos show under what the vehicle is doing, one shouldn't get pulled over if doing exactly the speed limit or 1 over.