title: Magento CE 1.8.1.0 grand total including tax is incorrect
body: <p>Hitting a brick wall here, for some reason Magento in the shopping cart is actually discounting the VAT from the total due. We are working with UK VAT (20%), and catalog prices include tax.</p>
  
  <p>In this example the subtotal including tax comes to £9.50</p>
  
  <p>So why on earth can the grand total including Tax come to £7.92? We haven't applied any discount to the item, so it's even more confusing. The grand total is worked out completely wrong for some reason.</p>
  
  <p>Data displayed in cart:</p>
  
  <pre><code>Subtotal (inc VAT)  £9.50
  Grand Total Excl. Tax   £6.34
  Tax £1.58
  Grand Total Incl. Tax   £7.92
  </code></pre>
  
  <p>Is this a confirmed bug in Magento CE 1.8.1.0 or is there a way to correct this?</p>