Round to five pairs:

1. If the first digit of the value to be discarded is greater than 5, it will be rounded to 1

2. When the first digit of the value to be discarded is equal to 5, and not all digits after 5 are zeros, it is rounded to 1;

3. When the first digit of the value to be discarded is equal to 5, and all the digits after 5 are 0, if the digit before 5 is odd, it is paired with 1. If the digit before 5 is even, it is discarded.