Auto update Sales Invoice Transaction

Hello All,

I need to know where should i write a code to Auto-Update Sales Invoice Transactions posted against a Sales Order. My requirement is whenever a Sales Invoice is posted with 'n' number of lines, a form should be Auto- Updated having the Sales Invoice Transaction Fields from Tables CustInvoiceTrans,TaxTrans_IN. I have written the code in CustInvoiceTrans Insert method, but i am not able to get some of the fields in the Form. Am i writing the code in wrong method? The encircled fields are present in TaxTrans_IN table but i am not able to get them in insert method of CustInvoiceTrans Table. Attached screenshot for your reference. Please suggest. Thank You.