Rounding makes numbers easier to read, but the point at which you round can change a result. Keep calculation precision and display precision separate when working through a small dataset.
Try three equal fractions
Suppose three values are each exactly one-third. Their exact total is one. If each is first rounded to 0.33 and then added, the displayed values total 0.99.
Neither page layout nor a calculator error caused the difference. The intermediate values were changed before the addition. This simple example does not imply that every real measurement is known exactly.
Keep precision tied to the data
Retaining more digits for a calculation does not mean a measuring instrument supports that many meaningful digits. Read the measurement documentation and describe uncertainty where relevant.
For a report, choose an appropriate display rule and apply it consistently. If rounded components do not add exactly to the displayed total, explain the reason when readers might be confused.
Make the sequence reproducible
Record whether you calculated from original values or already rounded summaries. A later analyst needs that distinction to reproduce the result.
Pair this exercise with small-number summary examples. A neat-looking answer should remain connected to the operations that produced it, including the seemingly minor decision about when to shorten the decimals.