Type the number by which you want the column multiplied in some spare cell.
Select that cell and copy it (Ctrl+C).
Select the cells you want multiplied.
Right-click, Paste Special
One of the choices is "Multiply". Do that. This replaces each value with value x N
To DISPLAY fewer digits (while leaving the underlying number unedited) you can click the "Decrease Decimal" button (looks like this:
To actually round the number in A1 to a certain number of digits (two digits in this example), use this formula in another cell: =ROUND(A1,2)
And here's an example of the difference between rounding to 2 decimal places and merely showing 2 decimal places. The sum in the "Show 2" column appears to be wrong. It's not, it's correctly summing the numbers including the non-displayed digits:
Understand...I usually use an example of 2 places and Round when I show an example of changing the price a certain %...interestingly over time there is little difference in the total but there can be real differences in individual items