To take off on Roy's great answer, the more common constructions use either the accusative or dative cases. 

"<s>During </s>Every evening we do the same." Here, there is an implied word, *during.* That's why "jed--" is not in the nominative case in German. Instead, there are two ways to render it.

*An jedem Abend* machen wir das Gleiche. We're using a preposition, "an," which makes jed--, jedem, putting it in the dative.

*Jeden Abend* machen wir das Gleiche. Here, jed-- becomes jeden, in the accusative, because there is no preposition.

Then there is the nominative example, 
*Jeder Abend* ist gleich. Every evening is the same.
(There is no implication of "during.") So "Jeder Abend" remains in its "original" (nominative) form.