These are all the number functions:
Truncation(), or Round() perhaps? - both can set the precision.
you should make sure the number format for the field on the layout is set to as entered, if you are calculating the decimal places.
CReate a copy of the price field. Use the inspector to format the number for three decimals and the other for two. Then use hide object of price > or =.20 for the three decimal field and hide object of price < .20 for the two decimal field. Then stack the fields.