A calculator often gives the result of a calculation to many
more digits than is required. Approximating to the answer
by giving it to a smaller number of significant figures or
decimal places is known as rounding off.
The result of rounding
is a shorter number having fewer non-zero digits yet similar
in magnitude. The result is less precise but easier to use.
The last digit to be ignored is the clue to how to round off
the last digit kept. If it is 5 or more, the last digit is
kept is increased by 1, if less than 5, it is unchanged. The
rounded number must be as near to the original as possible.
For example, 362.84518
362.8 when rounded to 1 decimal place;
363 when rounded to the nearest whole number;
362.85 when rounded to 5 significant figures;
360 when rounded to 2 significant figures.
73 rounded to the nearest ten is 70, because 73 is closer to 70
than to 80.