I received an additional 1099-B after filing. This adds an additional $76 to income, but actually represents a 20 cent short term loss. We were already receiving a full refund of taxes paid ($12), so this "loss" won't make any difference.
Do I still have to file and amended return for a 20 cent short term loss?
Even though it won't make a difference on your return, you should amend to account for the additional form that the IRS will be looking for. The IRS does not know your basis and if they may show the additional income as a short term gain based on the sales price.
But wait until the original return is fully processed before amending.
The IRS will get a copy of the Form 1099-B with the sales proceeds. Many times when they only get information about one half of the transaction (the sales price), they require you to inform them of the cost basis in order to show that you have a small loss. However, if your Form 1099-B shows a cost basis that will be reported to the IRS (the form should tell you), you should not have to amend anything at this time.