found a partial answer a long time ago, forgot to post the solution -
it depends on where you want the rounded number:
1) if in the tracker field called 'Numeric Field', you simply add a number (i.e. 3) to the box 'Decimal Places' in the tab 'Options for Numeric Field'.
2) if in the Mathematical Calculation field, than you add a set of parenthesis around your formula with the amount of places you want to round to, for example if I wanted to round to 4 decimal places and your formula was "(mul f_1080 f_1081)" than it would look like this:
(round(mul f_1080 f_1081)4)
this is explained on the Advanced Rating page in the documentation
Currently, adding or reducing the number of decimal places at the bottom of a TrackerList column ('compute') is not possible, hopefully this will be developed over time.