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):

:param final: if True, refunds will be generated if necessary
        :returns: list of created invoices
        """
        inv_obj = self.env['account.invoice']
        precision = self.env['decimal.precision'].precision_get('Product Unit of Measure')
        invoices = {}
        for order in self:
            group_key = order.id if grouped else (order.partner_invoice_id.id, order.currency_id.id)
            for line in order.order_line.sorted(key=lambda l: l.qty_to_invoice < 0):
                if float_is_zero(line.qty_to_invoice, precision_digits=precision):
                    continue
                if group_key not in invoices:
                    inv_data = order._prepare_invoice()
                    invoice = inv_obj.create(inv_data)
                    invoices[group_key] = invoice
                elif group_key in invoices:
                    vals = {}
                    if order.name not in invoices[group_key].origin.split(', '):
                        vals['origin'] = invoices[group_key].origin + ', ' + order.name
                    if order.client_order_ref and order.client_order_ref not in invoices[group_key].name.split(', '):
                        vals['name'] = invoices[group_key].name + ', ' + order.client_order_ref
                    invoices[group_key].write(vals)
                if line.qty_to_invoice > 0:
                    line.invoice_line_create(invoices[group_key].id, line.qty_to_invoice)
                elif line.qty_to_invoice < 0 and final:
                    line.invoice_line_create(invoices[group_key].id, line.qty_to_invoice)
        if not invoices:
            raise UserError(_('There is no invoicable line.'))
        for invoice in invoices.values():
            if not invoice.invoice_line_ids: