Arabic nominative and genitive cases are the definitions for the Arabic word when the word ends or is in a certain state. The other two cases are known as accusative and jussive.
Dhamma/Dhamma tanween represents nominative
Kasra/Kasra tanween represents genitive.
Fatha/Fatha tanween represents accusative.
Sukoon/Sakin (no vowel marking) represents jussive.