Inv appraisal NPV calculation- Decimal places to consider

Hello John! For eg when we calculate inflated sales price or variable cost how many decimal points do we take into consideration in the answers I have seen they round it up to the nearest whole number or it varies from 1-3 points, is there a specific decimal point we can take as a rule of thumb for convenience ? Because when I round it to the whole numbers they will consider it to 3 decimal points in the solution and vice versa leading to a big difference in answer because all the values change, I don't think the rounding up should matter but would love to hear it from you! Thanks