NPV

While calculating the NPV for a project, is it okay to round off all numbers to the nearest million?
The inflated variable costs, working capital increases, tax savings?
I have seen some answers that way rounded to the nearest million.
But some answers only round off the decimals to the nearest whole number.(in the BPP revision kit)
If you could please guide me.
Thank you in Advance.

I self study and i must include your lectures and notes have helped me alot.
I love the subject.Many thanks to you Sir.