PSU voltages

If there was, your computer wouldn't work. Or would be very unstable and would have died or gotten problems very quickly.

If you are worried about the slight variation (eg +12V at 12.8V), don't.

As enzo matrix said, there's nothing wrong with those readings. You can expect some minor fluctuations in the voltage levels; this is normal. However, if they seem to be way out then this is cause for concern although as enzo said, you would probably see stability issues beforehand.