So the way we do it, is that our Product class has:
belongs_to :account, :class_name => "Plutus::Account"
So if we have for example three widget products, like "big widget", "medium widget", "small widget", etc, they all belong to a Revenue account like "Widget Sales"
I'm not sure with tenants how you'd manage it, but I imagine you could create different sales revenue accounts types they could choose to apply to their products. We don't use tenancy here, but have separate databases for multiple SasS customers. We have them supply us with the account names they want, which we seed during setup, or manage for them behind the scenes if they need a new account.