The Ohm's law calculations of the parts do not agree with the whole
the most probable causses for the discrepancies are the following:


The DT830 is not known as a quality meter. Inaccuracies in the readings are one cause of the problem.
You are drawing almost 300 ma from a D battery. At that level the voltage of the battery will tend to drop fairly quickly. Depending on how fast you take the measurements, the readings can vary due to that factor. Note that your own readings show a 0.2 drop in voltage from no load to full load.
As a test of your meter try measuring the voltage of each of your D cells and compare it to the total voltage.