Rounding means that if the highest digit of mantissa is four or less, the mantissa will be removed; If the highest digit of the mantissa is 5 or more, the mantissa will be discarded, and the previous digit is 1. Rounding means one more digit than the reserved digit. For example, 3. 14 reserves one decimal place, that is, 3. 1. 3. 145 is reserved to two decimal places, namely 3. 15.