I have found that local (small-scale) vendors really appreciate payment in small bills because they don't have the capacity to make change all day long. So, when I go to Tana and frequent Score or other large establishments, I only take 10.000Ar bills and accumulate the change. When I get back to Maroantsetra, I can pay my preferred market ladies with "bundles" of 100Ar or 200Ar, which they greatly appreciate. Try it, you'll like the results.