Hi,

this is an example, but you can override existing function _compute_price used by the field price_subtotal ...

from openerp import api, models, fields

import openerp.addons.decimal_precision as dp

class AccountInvoiceLine(models.Model):

     _inherit = 'account.invoice.line'

     price_subtotal_tax = fields.Float(compute='_compute_price_tax', string=' Total including tax', digits= dp.get_precision('Product Price'), store=True)

    @api.one

     @api.depends('price_unit', 'discount', 'invoice_line_tax_id', 'quantity',

         'product_id', 'invoice_id.partner_id', 'invoice_id.currency_id')

     def _compute_price_tax(self):

         price = self.price_unit * (1 - (self.discount or 0.0) / 100.0)

         taxes = self.invoice_line_tax_id.compute_all(price, self.quantity, product=self.product_id,

                                                                                  partner=self.invoice_id.partner_id)

         self.price_subtotal_tax = taxes['total_included']

         if self.invoice_id:

             self.price_subtotal_tax = self.invoice_id.currency_id.round(self.price_subtotal_tax)

Bye