Regulation CC wouldn't apply to the check you've described because it was cashed and not deposited. If it had been deposited, however, Regulation CC's
http://www.bankersonline.com/regs/229/229-33.html §229.33(d) would require that you provide a notice of the return regardless of the amount (or of the notice, if received under §229.33(a)) by midnight of the banking day following the banking day on which you received the returned check (or notice). That requirement is satisfied by complying with the UCC's notice requirement.
If you fail to timely provide the notice required by Regulation CC or the UCC, and your customer ends up losing money because your delay, you could be responsible for losses sustained by your customer attributable to the delay (UCC 4-214).
When the check is cashed rather than deposited, your right to charge the item back to your customer's account may depend on state law outside the UCC and/or the terms of the customer's deposit agreement with you.