Nozturk,
"No sale" is a function of a cash register.
Nomrally, to open the money drawer of a cash register, you have to make sale, and it prints or displays the sale.
But sometime you want to open the drawer when there is no sales transaction taking place.
That's when you press the "no sale" key, and the word "no sale" is printed or displayed.
It has developed into an expression used to deny permission for something or to express disagreement.