Order header total tax calculation manipulation

Summary:

Hi Team, We would like to seek for your help to match our requirement where as you can see from the below screenshot in order screen at the header level we could able to view the total price , total tax and the pay now amount.

Our requirement is to show ,Pay Now value = Total price + Total Tax

= 320

But the header total should remain : 250 (as it is currently it is showing). Only the Pay now value to updated by adding the total amount. Is it possible to achieve this requirement, if yes,could you please guide us on how to achieve it?