As long as the wiring is a reasonable gauge, normal automotive etc. cable and not hair-fine stuff, the error should be minuscule.
The voltmeter probably draws something like 30mA, at a guess. At that, it would take over 60 foot total of 20awg wire to cause a 0.03V error.
Whatever the error is, it should be reasonably consistent, but depending on the internal voltage regulator in the meter.
The error margin is likely less than the reading accuracy or tolerance of the meter.
In other words, don't worry about it!