Luke 6:38 -"Give to other people, and you will receive. You will be given much. It will be poured into your hands--more than you can hold. You will be given so much that it will spill into your lap. The way you give to other people is the way God will give to you."
You wanted someone to read what you wrote on the receipt. You just didn't know it would be everyone. You may give God 10%, it doesn't entitle you righteous elitism. Just as the word of God spreads like a wildfire, so will this documented action.