I work as a volunteer for a tax exempt organization in the US. We are currently accepting donations in bitcoin but not issuing receipts for those donations. I would like to start issuing receipts. Is there any legal guidance available online about this? I haven't been able to find anything.
Using a Bitcoin payment processor like BitPay can make collecting donations as a charity much easier. BitPay will value the bitcoin at the time of the transaction, and charities can choose to take the payment as Bitcoin or have it converted to a number of other currencies and deposited directly in a bank account.
Of note, BitPay processes transactions for 501(c)(3) nonprofits entirely for free- no fees and 0% commission.
This may be the ideal solution for your situation, as it can also simplify legal complexities by allowing you to accept bitcoin donations as US Dollars. Then the procedure for bitcoin donations would be similar to your current procedure for USD donations.
To help make it possible for your donor to prove that the funds were indeed sent to your organization, a new feature known as the Bitcoin payment protocol, planned for release in version v0.9, will help with that.
The payment request can include information that alone could likely serve as the receipt for the donor.