Hi Partha
By default, unit amounts including prices, line discount amounts, and line charge amounts are maintained with a maximum of two decimals.
If you require the ability to enter, maintain, and view unit amounts with a maximum precision of six decimal points, you must extend the decimal point precision of the UnitAmountCur, UnitAmountMST, and CostPriceNonMonetary extended data types.
If you require a decimal point precision of more than four, you should also extend the PriceRoundOff extended data type.
Please refer to this article:
Microsoft Dynamics 365 Finance: Decimal Precision Options - Sikich LLP
And there is a similar discussion in the old thread:
(+) four decimal for price unit - Dynamics 365 Finance Forum Community Forum