Hi Yoga,
Ok, then you should be able to use the standard functionality.
In Transaction VOFM, and in the IMG, you should be able to find Pricing Condition Value Formula 141. You should use (or copy) that Formula in your MM pricing procedure, and follow the guidance given in the Formula code and the BAdI documentation mentioned there.
Additionally, you need to configure GTS to that the results of the calculations are copied into the correct Condition Types in your ERP schema. That configuration is under Customs Management > Calculation of Customs Duty > Assignment of Duty Types... > Assignment of Pricing Condition Type to Duty Type..
Good luck with the implementation.
Regards,
Dave