There is no law or regulation stipulating speedometer accuracy in the USA for anything but busses and commercial trucks where +-5% is the spec.
In Europe the requirement is that the speedometer never indicate less than actual speed, but up to 10% faster than actual is permissible. This must accommodate tire wear and variations in size of actual tires. Canada tends to follow Europe's lead.
As for odometer accuracy, it only has to be accurate enough to fend off class action lawyers if one is denied warranty service.
Working as a defense contractor prior to the Year 2000 Fiasco got roped into "Y2K Certification Testing." Mostly collected letters from OS and application vendors. Got labeled as troublemaker for asking for the Federal Standard For DoD Computer Clock Accuracy? All my reports stated, "If a problem occurs we will simply set the clock back 10 years because 1) there is no DoD standard or regulation that the computer clock be accurate, and 2) none of our applications need current time/date, we simply enjoy the ease of trusting the OS file timestamps and system logs."
2018 F-150 XLT SuperCab 4x4 2.7L
2016 Beta 430 RS
2016 Subaru Outback
2013 Tesla Model S 85
2009 Husaberg FE450
1983 Porsche 928S