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_id:
            return {'domain': {'product_uom': []}}
        vals = {}
        domain = {'product_uom': [('category_id', '=', self.product_id.uom_id.category_id.id)]}
        if not self.product_uom or (self.product_id.uom_id.id != self.product_uom.id):
            vals['product_uom'] = self.product_id.uom_id
            vals['product_uom_qty'] = 1.0
        product = self.product_id.with_context(
            lang=self.order_id.partner_id.lang,
            partner=self.order_id.partner_id.id,
            quantity=vals.get('product_uom_qty') or self.product_uom_qty,
            date=self.order_id.date_order,
            pricelist=self.order_id.pricelist_id.id,
            uom=self.product_uom.id
        )
        name = product.name_get()[0][1]
        if product.description_sale:
            name += '\n' + product.description_sale
        vals['name'] = name
        self._compute_tax_id()
        if self.order_id.pricelist_id and self.order_id.partner_id:
            vals['price_unit'] = self.env['account.tax']._fix_tax_included_price(product.price, product.taxes_id, self.tax_id)
        self.update(vals)
        return {'domain': domain}
    @api.onchange('product_uom', 'product_uom_qty')
    def product_uom_change(self):