Retainage option withoout PO

Good Day,

we are public compagny in the construction area. for the majority of our supplier, they bill with invoice hold back 10%.

i know that Retainage function is available in payable. However we donot use Complex PO. by the way we don not create any PO, the PO, and the complex payment term is handled by a subcontractor.

I need a why on how to performe retainag in AP Invoice without using PO.

i try the option to hold a partial amount for payment, but this way is not really my need. Because when we hold bakc 10% of the invoice, that taxe related to the invoice is calculting for only 90%, this is what i need excatly. i do not want that the taxe will be calculted for the whole 100%.