Does Abacus conform to IRS rules?
In the eyes of the IRS, a digital copy of a paper receipt is the legal equivalent of the original paper copy. You do not need to save the paper receipts; a digital photograph in Abacus is all you'll need.
Though it's usually a good idea (and easy!) to snap a photo of any paper receipts, for purchases under $75 a receipt image is not usually required by the IRS for proof of purchase.
For transactions over $75, the IRS requires that you save receipts (digital images in Abacus qualify).