Does the environmental argument really make sense?
Maybe all of the world's IT infrastructure could indeed account for 8% of total greenhouse emissions by 2025 (note that it is a prediction by greenies and I did not bother to check its accuracy). But that number is irrelevant, what matters is the environmental cost of a tiny sheet of paper versus the environmental cost of <1kb of data saved by the store and by your email provider.
A study by Carnegie Mellon came up with 7kWh/GB for storage and access of files in the cloud. Round up to 7e-3Wh or 25J per e-receipt (e-ceipt? Let's be hip!). A quick search yields numbers for paper production (without printing) of about 3MWh/ton. Low grade paper is something like 55g/m2. A medium sized receipt will then round up to 1g. Just the paper it's printed on is costing 3Wh or 11kJ. Someone should check this math (it's dangerously close to Friday) but that would suggest an e-ceipt is over 400 times more environmentally friendly than the paper that goes into a real receipt, to which you may add printing and disposal costs as well.