To report numbers in significant figures, Excel Help gives the following
formula and states that it is valid for numbers above zero:

=ROUND(B18,2-LEN(INT(B18))), where B18 is the number to round, and 2 is the
the number of significant figures desired.

In fact, it only works for numbers above 1, and if the number format is set
to 'general'

The formula works, but here's the problem: If the result ends in zero (e.g.
2.0), Excel only displays the last non-zero integer (e.g. 2). Since the last
zero is significant, this is a problem.