rounding numbers in multiple cells.

You could apply a number format with the desired
precision (e.g., 0.0), choose the Tools | Options...
menu command, and check "Precision as Displayed"
on the Calculation tab. Please note that this
will permanently alter the internal representation
of all numeric values on the worksheet to match
the precision of the number formatting. If you
don't want some of these values altered change
their number formatting to General before your
choose this option.