Last year, the government director Dr. Trips-Hebert explained the facts and the law to prevent misunderstandings like yours in the future. [1]
Let me translate the key section of his letter: "Section 86a of the Criminal Code is located in the third title of the first section of the Special Part of the Criminal Code.
The offenses of this title criminalize acts that constitute a 'threat to the democratic constitutional state.'"
The protected interests of the provision are political peace, the free democratic basic order
democratic basic order, the idea of international understanding, and Germany's reputation abroad.
The ban serves [...] to prevent the revival of the banned organizations or the aspirations they pursue [...]."
"Hitler.rocks" is not falling under this, since it is not a "threat to the democratic constitutional state". That's also why satire magazines like "Titanic" are allowed to publicly show Swastikas on their front page. [2]
A domain about hitler minerals [3] which does not aspire the revival of banned organizations such as the NSDAP, (there isn't any nazi glorifying content on the website), does not reflect a threat to Germany's democratic state. At least I hope so :)
[1] https://www.bundestag.de/resource/blob/869290/c8bd5f14ef172e...
[2] https://www.titanic-magazin.de/heft/2017/april/
[3] https://www.youtube.com/watch?v=yDVIrp8XaWI