Configuration:
- Company Currency: MXN
- Tax 16%.
- Multicurrency, MXN and USD.
- Decimal precision: 4
- Currency Data:
MXN: rate 1.0
USD rates

| Database time | rate | Local time (Mexico) | 
| --- | --- | --- |
| 2016-09-09 00:00:01 | 0.054440 | 2016-09-08 17:00:01 |
| 2016-10-11 00:00:01 | 0.051815 | 2016-10-10 17:00:01 |

Steps to reproduce:

1. Create an invoice for 600 USD  + tax (16%) with date 09/09/16 (September 9, 2016) and when you validate in the journal entry is $12,784.7172 MXN.
3. Create a bank statement in MXN and add a line with date 11/10/16 (October 11, 2016) and amount $13,372.80 MXN.
4. When reconcile select the invoice and there is a difference ($588.0828 MXN) add a line with the difference and select an account for the difference. 
<img width="607" alt="captura de pantalla 2016-11-04 a la s 17 23 26" src="https://cloud.githubusercontent.com/assets/6758279/20025385/749605a2-a2b3-11e6-8b1a-4e9fbf1521ed.png">

**Note that the amount of difference is $588.08 in when you select the account**

5. Click on reconcile.

Expected behavior:
- Reconcile the invoice and create account move.

Current behavior:
- Raise an error  `Wrong credit or debit value in accounting entry !`

![captura de pantalla 2016-11-01 a la s 19 18 52](https://cloud.githubusercontent.com/assets/6758279/19913537/1c272866-a069-11e6-9b06-5851681c7fa5.png)

addons/account_tax_cash_basis/tax_cash_basis.py
total_by_cash_basis_account[key] += amount
                        else:
                            total_by_cash_basis_account[key] = amount
                    if any([tax.use_cash_basis for tax in line.tax_ids]):
                        for tax in line.tax_ids:
                            line_to_create.append((0, 0, {
                                'name': '/',
                                'debit': line.debit_cash_basis - line.debit * matched_percentage,
                                'credit': line.credit_cash_basis - line.credit * matched_percentage,
                                'account_id': line.account_id.id,
                                'tax_ids': [(6, 0, [tax.id])],
                                }))
                            line_to_create.append((0, 0, {
                                'name': '/',
                                'credit': line.debit_cash_basis - line.debit * matched_percentage,
                                'debit': line.credit_cash_basis - line.credit * matched_percentage,
                                'account_id': line.account_id.id,
                                }))
        for k, v in tax_group.items():
            line_to_create.append((0, 0, {
                'name': '/',
                'debit': v if v > 0 else 0.0,
                'credit': abs(v) if v < 0 else 0.0,
                'account_id': k,
                }))
        
        for key, v in total_by_cash_basis_account.items():
            k, tax_id = key
            line_to_create.append((0, 0, {
                'name': '/',