The output from your inverter is a little different than the voltage from an outlet in your home. The voltage in your home is called a "sine wave", while the voltage from the inverter is a "modified sine wave". Due to this difference, some voltmeters can provide an incorrect reading.
To properly read the voltage from your inverter, a meter that measures True-RMS voltage is required. Other voltmeters will read low. Only a True-RMS voltmeter will correctly read 115VAC.
If it does not say "TRUE RMS" on the front of your meter, then it is not a True-RMS voltmeter and it will read up to 30 volts low. It will probably also provide inconsistent readings.