Currency precision without rounding

How can i let the currency precision on 5 without rounding.
This is an example of my issue:
i have an item price list rate is 12.5 and the customer have a discount of 35%,
So the rate of the item must be 8.2875 not 8.288.
How can i make the system not to round 8.2875 to 8.288 any help?

The value in the Rate field should not get rounded by itself. @rohit_w could you please review it once?