From the CBP- "Packages whose declared value is under $200 ($100 if being sent as a gift to someone other than the purchaser) will generally be cleared without any additional paperwork prepared by CBP. However, CBP always reserves the right to require a formal entry for any importation and generally exercises this option if there is something unusual about the importation, or if important documents such as an invoice or bill of sale do not accompany the item."

And this snippet- "The duty rate for many items typically bought in an on-line auction is zero, however, CBP may charge a small processing fee for mail imports that do require the payment of duty."



Reference: http://www.cbp.gov/xp/cgov/import/in..._purchases.xml