I don't know if an official standard exists, but most shops I've dealt with work to ±1/64" as the norm. Some have provided much closer tolerance, but involved extra cost due to more care & time being taken and more rejects being made.
It is not always possible to use floating nutplates & they usually look like crap anyway.
Here's an example of 'typical' tolerancing from a decent shop.
Thanks for that example Kelvin.