Calculate TVA amount in SAP T-Code: FB01

Note that T-Code: FB01 (Post Document) is known as Financial Accounting module under application component Financial Accounting and runs Documentation FI posting program SAPMF05A upon execution.

SAP TCODE                         :               FB01

Transaction Description:               Post Document

SAP Module ID                  :               FI

SAP Module Description:              Financial Accounting

You can refer SAP FI POST Document guide for more details.