There isn't a "generally recognized" limit as to what can be ignored, either on an original return or when a correction (amendment) is needed. Different taxpayers would have a different option on what is too small (or too large) to ignore.
If you fail to report a change in your return (e.g. a late-arriving or corrected tax form), the taxing authority may send you a notice later in the year asking about the omission.
For the IRS, this is not an audit - it is an automated Notice of Proposed Increase in Taxes.
They will calculate the tax due (plus interest and penalties) and you can send them a check. No amended return is necessary, so you won't have to upgrade.
The IRS uses this simplified procedure since It is extremely common to omit reporting a Form 1099-MISC. You file before they arrive, they get lost in the mail, get lost in your house or get tossed along with junk mail.
