 <p>The issue that I was having was a result of a bug involved with the sorting method implemented in Magento when ordering the total calculations. A more in-depth explanation and solution can be found at the following stack overflow thread.</p> <p><a href="http://stackoverflow.com/questions/9194281/sort-algorithm-magento-checkout-totals-sorted-wrongly-causing-wrong-shipping-ta">Sort algorithm: Magento checkout totals sorted wrongly causing wrong shipping tax calculation</a></p>