If a pilot is asked for a heading, giving it exactly or to the nearest five degrees will make little difference.
Personally, with Mode S available, I normally never ask for it. I can either just ask you to turn a number of degrees (and won't ask you to report new heading as I can see what it is if I need to), or I can do the maths and turn you on to a specific heading. Cuts down RT and superfluous info.
If you don't have Mode S or are out of cover of a Mode S radar, I would ask you to report your existing or new heading but only if I need to know it.