A customer of ours wants to customize the way in which the journal entries are created when a "Purchase" invoice is created. 

To better illustrate, let say I have the following Taxes & Journal

Puchase Tax ( Percentage on price) 20% - Accounting 1001

Withheld Tax ( Percentage on price) -10%  - Accounting 1002 ( This is a special form of taxation where the buyer withholds tax)

1001 - Tax on purchase 20%

1002 - Withheld Tax on purchase -10%  

3001 - Customer A

Say I have an invoice SO0001

 

1 x Product A  - Unit Price - EUR1000 

Tax 20% = EUR200

Withheld Tax -10% = EUR100

Payable amount = 1000 (Line Total) +200 (Tax 20%) - 100 (Withheld Tax -10%)

Total = EUR1100

And the following journal entries are created

1001 - Debit 200

1002- Credit 100

3001 - Credit 1100

This will balance our Journal to 1000 which is the pending earnings

However there is a requirement where the customer want the following entries created

1001- Debit 200

1002- Credit 100

*3001- Credit 1200 ( The price including tax)*

*9001- Debit 100 ( The witheld tax)(

So he wants the final price include the tax in the tax journal, and he wants an extra entry for the for the witheld tax credit.

How would I go about customizing that functionality. Either through custom code or through the UI configuration.

Is there any documentation we can read?