Our sales tax rate changed July 1, so I set up a new tax code for this new rate. I thought I double checked everything and it was working great until now, 3 months later when I ran a report to show the balance of account 2315 GST/HST Paid on Purchases and there was nothing there.

I dug into it and it turns out I made a mistake setting up the tax code and set it to not be reimbursable so the tax amount showed up as a second entry on the payable, but both amounts (subtotal and tax) were debited to whatever expense account the payable was assigned to.

I now have about 3.5 months of entries which are all incorrect.

My question is how to go about correcting this. One option is to "fix" the tax code, then adjust every entry to properly apply the tax amounts. My hesitation here is that when I adjust these I need to change the tax code and it will re-calc the tax amount. In theory these should be identical, but for many of my payables there are very small rounding errors which were edited to exactly match the vendor slip. Trying to adjust all these feels like a highly error prone undertaking. I am wondering if there is a cleaner approach?

Any suggestions would be greatly appreciated.