I have noticed that the energy consumption value on laser turrets appears to be truncated, from what I could see in the lua files each shot costs 800 kJ so the energy consumption is 800 kJ * FiringSpeed.
Right now my turrets have 3 + 2.7 attacks per second and should have 4.56 MW consumption but it is shown as 4.5 MW.
Here is a screenshot of this
Many of the GUI displays for numbers are only to 2 significant figures, or even floored to the nearest integer,
So this isn't a bug, but working as intended