Change Net Amount at Purchase Order Lines

Dear All,

I want ask about change/amend net amount at purchase order lines.

i buy some item, the quantity is 205, unit is liter.
unit price is 4.480146341

but we using 2 decimal, so the net amount = 918.40

our agreement with vendor is, the net amount is 918.43

i tried to typed the net amount manually, but its just make unit price blank.

how to amend the net amount without make unit price empty ?

i already make purchase agrement, but i still dont get net amount my user want ( 918.43 )

is there any work-around to correct the net amount without make unit price blank

Thank you