Caveat: most IBM business in Germany was done by its German subsidiary Dehomag, which can plausibly be regarded as a somewhat separate entity. IBM's dealings with the German occupiers in Poland were, however, done directly from New York.

IBM did business with the Nazi regime up until the US joined the war in December 1941. The systematic gassing of Jews started in December 1941 in the death camp at Chelmno in annexed Poland. No news of this new phase in the Nazis' anti-Jewish policies had reached the West at the time. Therefore, it is fair to say that IBM did not directly and knowingly aid the Nazis in the industrial-scale killing of the Jews of Europe.

However. IBM technology facilitated record keeping for the Nazi regime. The Nazi regime kept records on everything. Among the many things the Nazi regime kept records on were the following that relate to the Holocaust: the ethnicity and addresses of German citizens, and later, the ethnicity and addresses of citizens of German-occupied countries; the personal details of concentration camp inmates; and railroad timetables in Poland (where the death camps were located which were supplied with victims by train). It is not clear to what extent IBM executives connected the dots between their fancy punch card technology and the oppression of the Jews and the Nazis' political opponents. It is clear that the dictatorial nature of the Nazi regime was a known fact, and that IBM did business with them in occupied Poland.

Personally I wouldn't say that IBM is responsible for millions of deaths. The Nazis were responsible for those. IBM does bear the guilt of doing business with a violent and oppressive regime. But such is business and the same goes on to this day all over the world.