Security unit price decimals

Guys,

We have a security account in foreign currency where unit price is maintained with 6 decimal digits. When security is sold on unit price, the system calculates a small price difference. This small amount of security price seems to be a rounding error, since the price difference value = sold quantity * (unit price calculated with 8 digits - unit price calculated with 6 digits).

Have you ever faced a similar case? How can we eliminate this price difference?

Thanks,

Adina