Thanks for taking the time to answer, but I don't get why should I opt-in to double entry bookkeeping. For someone who wants to build a side-project this is the last thing I want to think about.
Also, if you track sales in euros and dollars, then how do you track the changes in the exchange ratios?
What about rest? What happens to the data you aggregate? It just sounds like more work for me to make it available to my accountant.