Consider the following question from 新完全マスター文法 (N3):
（ ）笑わなくてもいいじゃありませんか。
a いくら
b そんなに
c どんなに
According to the theory associated with the exercise:
いくら should be followed by ～ても／～でも
そんなに should be followed by ～ない
どんなに should be followed by ～ても／～でも
However, when we look at the question above, the example sentence includes both ～ても and ~ない. According to the answer key, そんなに is the best answer... but why?
Well, this may not be a very good question if there is not enough prior context. Saying いくら/どんなに笑わなくても is also perfectly grammatical, and actually makes sense in a certain context.
- そんなに笑わなくてもいいじゃありませんか。
You don't have to laugh like that.
(Please, don't laugh at me like that!)- いくら笑わなくてもいいじゃありませんか。
どんなに笑わなくてもいいじゃありませんか。
No matter how [someone] won't laugh/smile, that's okay, isn't it?
(Being unwilling to smile is not a problem, huh?)
The latter would make sense, for example, when you are protecting a person who stubbornly refuses to smile in front of a TV camera.
Still, in a test like this, you are expected to give the most "likely" answer, so I will definitely choose そんなに if I had to choose one.
Wait a little and someone else will give you a proper answer but here's something to get you started in the meantime. This is not exact but generally works.
そんなに：That (much)
いくら~ても/でも：No matter how (much)
どんなに～ても/でも：No matter how(ever) (much)
So using your example,
a You don't have to laugh how much (x)
b You don't have to laugh that much (o)
c You don't have to laugh however much (x)
Some other examples of 「そんなに」 use:
「そんなに食べたら太るわよ。」→ You'll gain weight if you eat that much.
「え。。。そんなに痛かったの？」→ Wait...It hurt that much?
「そんなに美味しいとは思えないけど。」→ I don't think it tastes that good.
Compare with examples of 「どんなに」：
「どんなに痛くても我慢しろ！」→ Bear with it, no matter how much it hurts!
「どんなに美しい人でも変顔はうける」→ No matter how beautiful they are, their weird faces are funny
「どんなに高い山でも登り続けたらいつかは越えられる。」→ No matter how high the mountain is, if you keep climbing you'll eventually overcome it.
Examples of 「いくら」：
「いくら寝ても寝た気がしないの。」→ No matter how much I sleep, it doesn't feel like I slept.
「いくら払ってもこれは売らないぞ！」→ I ain't selling this, no matter how much you pay!
「いくら食べても食事代は一緒なんて信じられない！」→ That the price of the meal remains the same no matter how much you eat is unbelievable!
Now, be careful not to confuse 「どんなに」 with 「どれだけ」(frequently used as 「どんだけ」), because it's completely different in nuance even though translation is still "how much".
「１００円寿司で２万円？？どれだけ食べたの？？？？」→ 20,000 yen at a 100 yen sushi restaurant?? How much did you eat????
「２千円のアニメフィギュアを１万円で買ったと？！どんだけ欲しかったの？！」→ You bought a 2000 yen anime figure for 10,000 yen?! How much did you want that thing?!
