architecture – TransactionScope in DAO or in BLL (Business Logic Layer)?

I’ve been working with Entity Framework, Repositories, Unit of Work, DDD, CQRS…

But I have an different challenge now…my company is working in the below architecture:

Contrllers -> BLL (Business Logic Layer) -> DAO with raw sql connection…

I have to insert a Customer with many dependents. I have a DAO for Customer and another for Dependent. So, I will insert in two tables…

I now how to use TransactionScope, how it works…But…what’s the best practice? Using TransactionScope in Business Layer? In DAO?

I have CustomerDAO, CustomerBO…where should I put the transaction scope? some people say to create a service class, but is it the same of CustomerBO?