When you create a Purchase Invoice the Price and Approved Quantity are multiplied to give the Amount Approved.
However, the Unit Price is calculated by dividing the Amount Approved by the Approved Quantity if you adjust the Amount Approved directly. In some cases, the calculate Price may not be rounded to the desired number of decimal places.
You can go to File -> Configuration Manager -> Inventory -> Inventory Options. Adjust the Max decimals for Unit Cost Calculations to provide the proper calculated price. We recommend at least 5 decimal places when using multiple units of measure.