Okay. The answers give above are correct, but it is a bit tricky to understand.
In facts, there is only one "reroll" in the rules : the dices rolled again due to a CBT value > 5.
Once all your rerolls have been done you have your number of hits made.
Then you have some effects that force you to roll again some dices that occurs a v
Hit. As they roll a "hit dice" they are not what the rules calls "rerolls".
In the facts, Cursed X/Y works exactly like if the cursed unit gives Man at arm X to its opponent in close combat... so a cursed X unit that fight a man at arm Y unit Will only increase the level of man at arm from Y to Y + X... but again, a dice that scored a hit can only be rerolled once. So a cursed 3/3 again a man at arm 5 will have in facts no effects bigger than the man at arm 5 :-)
[EDIT] curse X increases the level of man at arm.
But just to be sure let me ask using a example.
Enemy cursed 3/3 vs my model with man at arms 5.
The enemy scored 3 hits, he rerolls this hits resulting in (1,3,5) vs my defense wich is 3. so he scores 2 hits and its the end of our combat (Even if we potentially had 8 rerolls, cursed 3/3 + man at arms 5, and we just used 3 of them). Right?