Answer:

In a calculation the numbers used are often approximate, as when they represent lengths measured to the nearest centimeter. When this is the case, the result of the calculation may be rounded off to an appropriate number of decimal places that is the number of figures to the right of the decimal point after the rounding process.

When rounding off, the last figure to be kept is increased by 1 or left as it stands depending on which the number is nearer to. For example, 32.8632 is nearer to 32.86 than 32.87 so to 2decimal places it is rounded to 32.86. But 32.8682 is nearer to 32.87 than 32.86 so it is rounded to 32.87 to 2 decimal places.

The size of the figure immediately to the right of the ones to be kept is critical. If it is 5 or more then the remaining right-hand figure is increased by 1. If it is 4 or less, then all the remaining figures are unchanged.

The following examples illustrates what may happen:
4.9528 becomes 4.953 to 3 decimal place
4.95 to 2 decimal place
5.0 to 1 decimal place