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The Berliner Volksbank at Mehringdamm has a loose coin accepting machine. If you take the U6 or know the area, its the direction where the Finanzamt is. I discovered that when I went to make a deposit for my business. We literally have kilos of small coins collected over the years, and other branches adamantly refused to deal with them even though they're supposed to. I don't know if you need to have an account, however.