Some questions require entry of a number, and I'm sure for these CASA will grade allowing for minor (ie. immaterial) discrepancies where appropriate.

For example, the EoD and BoD charts in the AIP are clearly marked in 5 minute intervals, so if you were doing a time calculation then you shouldn't be more than 1 or 2 minutes out and this would seem to be an immaterial discrepancy, IMHO. A couple of degrees variation when calculating heading (given track and wind) would also seem immaterial (who can fly perfectly along a heading with less than 1 or 2 deg variation, anyway). If calculating track given map positions, then an allowable discrepancy would depend on distance (extrapolation is a handy technique in this regard). For take-off and landing distances, get a very sharp pencil and you should be within 100'/50m

On the other hand, you may get a question where no discrepancy is appropriate. For example:This is just maths, so you can provide a perfectly precise answer.

You're asking good questions... a detailed (and prepared) mind generally will do quite well in the PPL exam!