Try using the ROUND function which you can find in the SSI Script library.
Example ...
[%ROUND(Q1,2)%]
This will display the number entered at Q1 to 2 decimal places. It will round to the 2nd decimal place which is nice.
Other functions to consider are ...
FORMATNUMBER (NUMBER,"ThousandsSeparator", "DecimalSeparator", NumDecimalPlaces)
ROUNDTONUMBER (NUMBER,ROUNDTO,#DECIMALS)