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):

'''
        This function returns an action that display existing vendor bills of given purchase order ids.
        When only one found, show the vendor bill immediately.
        '''
        action = self.env.ref('account.action_invoice_tree2')
        result = action.read()[0]
        
        result['context'] = {'type': 'in_invoice', 'default_purchase_id': self.id}
        if not self.invoice_ids:
            
            journal_domain = [
                ('type', '=', 'purchase'),
                ('company_id', '=', self.company_id.id),
                ('currency_id', '=', self.currency_id.id),
            ]
            default_journal_id = self.env['account.journal'].search(journal_domain, limit=1)
            if default_journal_id:
                result['context']['default_journal_id'] = default_journal_id.id
        else:
            
            result['context']['default_journal_id'] = self.invoice_ids[0].journal_id.id
        
        if len(self.invoice_ids) != 1:
            result['domain'] = "[('id', 'in', " + str(self.invoice_ids.ids) + ")]"
        elif len(self.invoice_ids) == 1:
            res = self.env.ref('account.invoice_supplier_form', False)
            result['views'] = [(res and res.id or False, 'form')]
            result['res_id'] = self.invoice_ids.id
        return result
    @api.multi