Currently studying for my Nav exam, and am dismayed that the mock exams are asking for mag hdg to 1 degree accuracy - sometimes with my answer splitting two of the four choices.
I'm in the same position, planning to sit the exam this weekend. I've noticed that that my headings consistently fall 1-2 degrees on the + side of the mock answers, so when I have to choose between two answers I've used this to decide which one to go for and it seems to work. Hopefully it will on the day anyway!
Good luck.