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
"""
        Compute the total amounts of the SO.
        """
        for order in self:
            amount_untaxed = amount_tax = 0.0
            for line in order.order_line:
                amount_untaxed += line.price_subtotal
                amount_tax += line.price_tax
            order.update({
                'amount_untaxed': order.pricelist_id.currency_id.round(amount_untaxed),
                'amount_tax': order.pricelist_id.currency_id.round(amount_tax),
                'amount_total': amount_untaxed + amount_tax,
            })
    @api.depends('state', 'order_line.invoice_status')
    def _get_invoiced(self):
        """
        Compute the invoice status of a SO. Possible statuses:
        - no: if the SO is not in status 'sale' or 'done', we consider that there is nothing to
          invoice. This is also hte default value if the conditions of no other status is met.
        - to invoice: if any SO line is 'to invoice', the whole SO is 'to invoice'
        - invoiced: if all SO lines are invoiced, the SO is invoiced.
        - upselling: if all SO lines are invoiced or upselling, the status is upselling.
        The invoice_ids are obtained thanks to the invoice lines of the SO lines, and we also search
        for possible refunds created directly from existing invoices. This is necessary since such a
        refund is not directly linked to the SO.
        """