In the B2B world where quantities are high, item price/cost can get detailed to the thousands place, ie Widget cost is $0.753 per unit. This is not asking for dynamic currency conversion - just the ability to allow the price/cost of an item to be 3 decimal spaces. Then when calculating the total due for that line and total bill, standard rounding to be used for total $.
Guest
additional comment - while I stated in B2B world, the 3 decimal spaces for price/cost of item should be available for all merchants