That 0.01 Ohm shunt resistor in the meter and the test leads, even 14 ga leads, can affect your measurements and calculations. I had come across this before and it is the reason I posted this about constructing an external shunt resistor. I was measuring 15A and the voltage drop across the test leads and the .01 ohm shunt in the meter really took a toll. I made an external shunt of only 0.001 Ohm.
At 5A you are probably dropping 0.1V across you meter and leads. That would be 0.5W of lost energy.
If you don’t want to bother with making one, Cereal-Killer sells one already made.