There is no one answer to this question, as Taco Bell has different promotions and events going on at different times. However, Taco Tuesday is generally a day where customers can get free tacos if they buy any other item.
In recent years, Taco Bell has offered a variety of different deals and promotions on Taco Tuesday, including free Doritos Locos tacos with the purchase of a Crunchy Taco, a free Chalupa with the purchase of a burrito, and free nachos with the purchase of any entrée. In general, it seems that Taco Bell does have Taco Tuesday, though the promotion and events vary from location to location.