Here is the IRS' guidance on de minimis:
Effective for taxable years beginning on or after January 1, 2016, the Internal Revenue Service in
Notice 2015-82
increased the de minimis safe harbor threshold from $500 to $2500 per invoice or item for taxpayers without applicable financial statements. In addition, the IRS will provide audit protection to eligible businesses by not challenging the use of the $2,500 threshold for tax years ending before January 1, 2016 if the taxpayer otherwise satisfies the requirements of Treasury Regulation § 1.263(a)-1(f)(1)(ii).
Here is the entire cite from the IRS:
