Impacted versions:

[9.0]
Tested in runbot http://174550-9-0-10dcec.runbot10.odoo.com/

Steps to reproduce:

Set the Tax Calculation Rounding Method to "Round Globally" 
Create a Sales Order with the following lines with 7% taxes

1) 5,095.20 
2) 523.20 
3) 80.64 
4) 54.12 
5) 182.00 
6) 186.20 
![image](https://cloud.githubusercontent.com/assets/16055718/19144073/309aa082-8bda-11e6-81d0-2461c4e9a467.png)

Create a Sales Invoice with the same lines with 7% taxes
![image](https://cloud.githubusercontent.com/assets/16055718/19144078/38048b58-8bda-11e6-9c2b-4b501cfa1e12.png)

Current behavior:

The total taxes in Sales Order are $477.48 

The total taxes in Sales Invoice are $477.50 

Expected behavior:

Both the total taxes in Sales Order and Sales Invoice should be 477.50 

Video/Screenshot link (optional):

addons/sale/sale.py
if not self.product_uom:
            self.price_unit = 0.0
            return
        if self.order_id.pricelist_id and self.order_id.partner_id:
            product = self.product_id.with_context(
                lang=self.order_id.partner_id.lang,
                partner=self.order_id.partner_id.id,
                quantity=self.product_uom_qty,
                date_order=self.order_id.date_order,
                pricelist=self.order_id.pricelist_id.id,
                uom=self.product_uom.id,
                fiscal_position=self.env.context.get('fiscal_position')
            )
            self.price_unit = self.env['account.tax']._fix_tax_included_price(product.price, product.taxes_id, self.tax_id)
    @api.multi
    def unlink(self):
        if self.filtered(lambda x: x.state in ('sale', 'done')):
            raise UserError(_('You can not remove a sale order line.\nDiscard changes and try setting the quantity to 0.'))
        return super(SaleOrderLine, self).unlink()
    @api.multi
    def _get_delivered_qty(self):
        '''
        Intended to be overridden in sale_stock and sale_mrp
        :return: the quantity delivered
        :rtype: float
        '''
        return 0.0
class MailComposeMessage(models.TransientModel):