It can also be specified as a shunt resistance. This is for my Simpson 467:Is there another term for that parameter?
This is how meter perturbation is corrected for my Fluke 27:
The bottom line is that no meter is ideal and you can avoid hassle by calculating current instead of measuring it. I assure you that can trust Ohm's Law.
There are times when the non-ideal nature of voltmeters can also affect readings, but in your experiment, your voltmeter isn't introducing any meaningful error.