Rounding in examiners report

[roboto100]

So; throughout the year my class has been told not to round until the very end of the question (standard practice to avoid rounding errors). But i've been noticing in the examiner's report that sometimes this results in incorrect answers.
Sometimes it's just more accurate (14.14 instead of 14.1), other times it's not much of an error (3.46 instead of 3.4) but sometimes it gets unreasonable (23.8 instead of 25).

Is there some universally accepted method of rounding that we're meant to follow? And are we likely to get marked wrong for an answer that differs from what the examiners have, simply because we've used more accurate numbers?
Thanks for any help in advance.