Round off after every question?

Ok so you guys know how in physics there are trailing questions, where you take the answer from (a) (i) in (a) (ii) calculation for example.

This applies to Biology and Chemistry too.

Basically I have a habit of doing all calculations, as in keeping the raw values and finishing the whole question.

Then finally I round off to 3 s.f. or whatever and write the answer in the space.

And sometimes its fine because the marking scheme has a range. But sometimes my answers are occasionally wrong, not too wrong, but a bit off. And I found that if had used the rounded off values for trailing questions it would be alright.

So what's the proper way? Round off after every question, and use that value? Or calculate using raw values and round off at the end?