Tax Calculation using gross price

Hi all,

We are doing the configurations of Peru Localization (TAXPE Tax Pricing Procedure). Due to legal requirements we did the following configuration of PO Pricing procedure:

Gross Price: 100,00

Net Price:       82,00

Tax Base:     100,00

Tax Rate:       18%

Calculation: 100,00 * 18%

Tax Amount: 18,00

The PO pricing procedure calculates the net price. After that, the tax procedure TAXPE is called.

However the system is assuming the net value as tax base as you can see below:

Do anyone knows how to make SAP calculate the tax amount using net amount + tax (tax included in gross price).

Thanks

Gian