Transitioning PowerBI report from tabular data to using row-level data

You could use calculation items applied to the whole report along the lines of this:

VAR Val = SELECTEDMEASURE ()
RETURN
    IF ( Val > 0 && Val < 5, 1, Val )

This should still treat zeros as zeros.

It's harder when you have percentages too because you need a way to distinguish which measures are which. If everything is either a count or a percentage then you could deal with it like this:

VAR Val = SELECTEDMEASURE ()
RETURN
    SWITCH (
		TRUE (),
		Val = 0, 0,
		Val < 0.05, 0.01,
		Val IN { 1, 2, 3, 4 }, 1,
		Val
	)