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):

return self.env.user.company_id.sale_note
    @api.model
    def _get_default_team(self):
        default_team_id = self.env['crm.team']._get_default_team_id()
        return self.env['crm.team'].browse(default_team_id)
    @api.onchange('fiscal_position_id')
    def _compute_tax_id(self):
        """
        Trigger the recompute of the taxes if the fiscal position is changed on the SO.
        """
        for order in self:
            order.order_line._compute_tax_id()
    name = fields.Char(string='Order Reference', required=True, copy=False, readonly=True, states={'draft': [('readonly', False)]}, index=True, default=lambda self: _('New'))
    origin = fields.Char(string='Source Document', help="Reference of the document that generated this sales order request.")
    client_order_ref = fields.Char(string='Customer Reference', copy=False)
    state = fields.Selection([
        ('draft', 'Quotation'),
        ('sent', 'Quotation Sent'),
        ('sale', 'Sale Order'),
        ('done', 'Done'),
        ('cancel', 'Cancelled'),
        ], string='Status', readonly=True, copy=False, index=True, track_visibility='onchange', default='draft')
    date_order = fields.Datetime(string='Order Date', required=True, readonly=True, index=True, states={'draft': [('readonly', False)], 'sent': [('readonly', False)]}, copy=False, default=fields.Datetime.now)