Yes, you have to login for each round of voting. However, you can use the same voter credentials for each ballot and announce the URLs for each ballot in a single e-mail invitation. This makes it easier for voters to login, easier to manage the various rounds, and a result can be downloaded after each round. Please note, however, that an online election consists of just one round of voting, even if several ballot papers are used. In order to produce multiple rounds of voting, you have to create multiple online elections.
As part of POLYAS Live Voting, you can also create multiple ballot papers. In this case, the vote per ballot paper is carried out in a separate voting round. In this case, however, your voters only need to login once.