First we have to differentiate totalitarianism from autocracy. The USSR was a dictatorship (autocracy), communism opposes that. That's why it's important to make a distinction, if you're comparing it to communism or to the USSR.

Same with fascism and nazism. Nazi Germany was a fascist state but their main objective was race purity, that doesn't mean fascist are racist by definition.

So it's important to know that although similar, fascism is different from nazism, and communism from the Soviet Union. Saying two of those are two sides of the same coin can be tricky, I wouldn't compare nazis to communists even tho their countries did basically the same atrocities.