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):

_inherit = 'product.template'
    track_service = fields.Selection([('manual', 'Manually set quantities on order')], string='Track Service', default='manual')
    @api.multi
    @api.depends('product_variant_ids.sales_count')
    def _sales_count(self):
        for product in self:
            product.sales_count = sum([p.sales_count for p in product.product_variant_ids])
    @api.multi
    def action_view_sales(self):
        self.ensure_one()
        action = self.env.ref('sale.action_product_sale_list')
        product_ids = self.product_variant_ids.ids
        return {
            'name': action.name,
            'help': action.help,
            'type': action.type,
            'view_type': action.view_type,
            'view_mode': action.view_mode,
            'target': action.target,
            'context': "{'default_product_id': " + str(product_ids[0]) + "}",
            'res_model': action.res_model,
            'domain': [('state', 'in', ['sale', 'done']), ('product_id.product_tmpl_id', '=', self.id)],
        }
    sales_count = fields.Integer(compute='_sales_count', string='# Sales')
    invoice_policy = fields.Selection(
        [('order', 'Ordered quantities'),
         ('delivery', 'Delivered quantities'),
         ('cost', 'Invoice based on time and material')],
        string='Invoicing Policy', default='order')