why does my voltage regulator produce 5.11 volts instead of 5?
If you look in the datasheet you find that the output voltage of the 7805 can vary between 4.8 and 5.2 volt. This is the error margin of the output voltage.

Remember that in every design there is always an error. So the regulator can be off and/or your multimeter. Even the ruler to measure a distance is not 100% accurate. We can decrease an error but at the new level you find an error again.

As far as your DC input is concerned you need at least 7.5 V input to obtain a stable regulation. This again according to the datasheet.