LaTeX templates

[Giedrius <..hidden..>]

I would like to change a LaTeX template for invoices. It is necessary
for me, when I put a tick on checkbox "Tax Included" in the form of
"Add Sales Invoice" it should be shown:
- the price of the goods without the tax was displayed in a column
"Price";
- the sum of the goods in line without the tax was displayed in a
column "Extended";
- the sum of all goods without the tax was displayed in a line
"Subtotal";
- also I need that a total sum of the discount would be shown in the
invoice.

Example:

Price of sold parts (Tax included):
Bread - $2.36
Butter - $8,26
Milk - $4.72

Desirable printed output of invoice:
Pos Number Description Qty Price Disc\% Extended(Amount)
1     0001      Bread          10   $2      10%    $18.00
2     0002      Butter           5    $7                 $35.00
3     0003      Milk             2    $4       5%       $7.60
_________________________________________________
                                                    Subtotal:   $60.60
                                                VAT(18%):   $10.91
                                                         Total:   $71.51
--------------------------------------------------------
                               Total whitout discount:  $74.34
                                         Total discount:  .$2.83	

Thanks for the help.
-- 
Giedrius