Tonight I went to the local D2 - it's kind of the cleaning, petfood, stationery, storage and hardware section of a supermarket. (No food except chewing gum.) I bought quite a few things - new brake pads for the bike, detergent, shampoo, futon clips, garbage bin deoderizer, canisters of gas and other such household basics - about 20 items in all. In the interests of being socially aware and environmental, I took my own bag.
I will keep taking my own bag and practice saying 'no thanks' more successfully.
Stuck by D2
(As a contrast the supermarket up the hill from there charges 8 yen or so for each bag and there is no tape happening there.)