Missing Totals in Magento, and Mage_Tax
This is a pretty simple problem, but when I was searching around for it, I didn’t see any reference to my particular resolution, so this is mainly to help in case anyone else experiences the same problem.
I recently had a problem with Magento in which it seemed in the Cart and during the onepage checkout, the area showing the subtotals and the grand total had suddenly gone missing. After more hunting around than I care to admit, I ruled out a problem with the store’s theme, since another store set to the same theme had no such problem. Most configuration options were also identical, which ruled them out as the cause as well.
So, assuming it was a configuration problem, I started going through and comparing. In the problematic store, several modules are disabled, so I started turning them back on, just to rule out that as a possibility. The working store had everything still at the site defaults. It turns out that the problem was simply that Mage_Tax had been disabled. Re-enabling it immediately made the subtotal and grand total reappear. To me, at least, this doesn’t seem very obvious or intuitive, but that’s what it was.