Ed,
It may be due to the resolution of your system. For instance my controller is ½ step and with 4tpi lead screws each step is 0.000625 inch. So if the G-code is in 4 or 5 decimal places it is unlikely that Mach can drive to that exact position. Mach will drive to and display the step that is the nearest to the commanded G-code. For example if I step in 0.001 increments the DRO will show steps such as .0000, .0006, .0019, .0025, .0037, .0050…. etc. As you suspect it’s quite likely normal and not a poblem.
Al