PriceField tax_amount should not be rounded

In Quebec, we have a combined tax rate of 14.975%. CiviCRM rounds this to 15%.

How to reproduce:

• Create a tax of 14.975
• Create a priceset with a text field of 1$
• CiviCRM will display: 1$ + 0.15$ Sales Tax
• Enter 100$ in that field, and CiviCRM will calculate 15$ taxes.