Is it permissible to sell musical tapes in a shop, and what is the ruling on the money earned from selling them, and does refraining from selling them constitute disobedience to parents?

It is not permissible for you to sell or buy music tapes, and it is not permissible to obey your parents in this matter, due to the Prophet's (peace be upon him) saying: "There is no obedience to a created being in disobedience to the Creator." You can work in the bookstore by buying and selling items other than music tapes. You should advise your parents and explain the Sharia ruling to them gently, kindly, and wisely.