New precision tuning-devices are on the market, while some electronic organs have their own tuner built right in. With the violin family, tuning is mental habit instead of a hardware gadget. Piano tuners are taught how rather than why, and it takes about six months to master a routine which is something like a religious ritual, and which cannot be transferred to a non-twelve system. These tables can be calculated to better than one part in a million on computers, but nobody in their right mind would expect that kind of accuracy on real guitars. Your friendly tone-bender in the rock band wouldn't even want it if he could have it.
People buy all kinds of magic effects-boxes to keep the tones from being too steady, too dead.
Synthesizers and electronic organs have all kinds of special circuits invented for them to liven up the tone, to loosen the tolerance. So a specific percentage tolerance for even the 12-tone equal temperament tuning is pretty much an exercise in futility. A very careful maker might be lucky enough to position the frets that well most of the time, but that would not guarantee such precision in the pitches actually heard from that guitar in a real performance. More about that in a moment. Musical notation makes this even more complicated.