Which of the following sentences is correct?
(1) I'll go shopping if it has stopped raining.
(2) I'll go shopping if it will stop raining

In number one, you should use matching verb tenses - "I will" does not match "it has."

Number two is ok, but I would probably say: I'll go shopping if it stops raining.

If you want to use the past tense "has" you could say, "Since it has stopped raining, I'll go shopping."

I hope I didn't confuse you more on this.