At Seibu, a Japanese market, they charged 5 yen per bag last time I was there.  Might be more now.  I was told this is the policy at all markets to encourage customers to bring their own bags, which many did.  I later purchased a couple of the "permanent" bags to use and as a souvenir.  Difference though, is that there is hardly any litter in Japan because they have a massive recycling program and very few trash cans.  If you have trash and there are no receptacles, you carry it with you until you find one, usually at convenience stores.