0.5 – Round Up or Down?

I remember in Maths the rule was to always round 0.5 up.

So, for instance, 5.5 would be rounded to 6.

Going through the F6 books (Kaplan), I’ve found that 0.5 is sometimes rounded up and at other times rounded down.

Looks to round up or down is based on which option reduces tax liability.

For instance, when multiplying by 32.5% or 37.5% for dividend income (which sometimes leads to a figure ending in 0.5), the value is always rounded down (e.g. 5339.5 to 5339).

In other cases, where the amount is a deductible and reduces tax liability, it is rounded up (e.g. 5339.5 to 5440).

Just wanted to ask if there’s any specific rules about this? Is it necessary to round 0.5 in a way that reduces tax liability? What are the general rules for rounding in taxation? Before this I always thought 0.5 should ALWAYS be rounded up.

Also, I’ve found that where the figure is slightly higher (0.53 for example), then it is always rounded up as is normal.

Anyway, just wanted to ask if this is some rule that the examiner marks. One answer of mine differed from the Kaplan answer by 1 because I rounded 0.5 up whereas the Kaplan book rounded it up.