Let me say that all income should be reported on your tax return.
That said, if the additional $20.90 in dividend income did not cause any change in your taxable income or tax, I would not file a Form 1040X. Please understand that the IRS eventually runs a matching program against the Copy A that they receive of all the Forms W-2 and the Form 1099 series. Notices are routinely sent to the recipients of forms that were not reported on tax returns. So, later this year, you will probably receive a notice from the IRS about the missing form. Since you can honestly reply that you ran your tax return with the additional income and no additional tax was due, that explanation should satisfy the IRS.