The standard rules for rounding off are well known. Before we set them out, let us agree on what to call the various components of a numeric value.
The most significant digit is the left most digit (not counting any leading zeros which function only as placeholders and are never significant digits.)
If you are rounding off to n significant digits, then the least significant digit is the nth digit from the most significant digit. The least significant digit can be a zero.
The first non-significant digit is the n+1th digit.
Rounding-off rules
If the first non-significant digit is less than 5, then the least significant digit remains unchanged.
If the first non-significant digit is greater than 5, the least significant digit is incremented by 1.
If the first non-significant digit is 5, the least significant digit can either be incremented or left unchanged (see below!)
All non-significant digits are removed.