The early Principate Romans were not as interested in converting their subjects as modern religions are, so be sure to neutralize that bias from your interpretation of Roman behavior.
Romans were relatively tolerant of barbarian religions. Although Romans found it mildly offensive for the Jews to claim that only one God existed, they had incentives to be flexible. Being flexible meant implementing an additional tax on Jewish worshipers and being inflexible would result in uprisings, so the Roman state decided to guarantee freedom for Jews to practice their religion.
Roman non-state writings overall show mild bemusement at the Jews' insistence that only one God existed and that he had nothing to do with the Roman Emperor. The Romans were not really concerned with theological challenge that this presented. Neither were the Jews in a position to argue about whether the tax on Jewish synagogues was a roundabout way of funding public ceremonies for other deities than the Jewish God.
The implementation of the taxes on Jews (Fiscus Iudaicus) originally replaced the tithes that Jews paid to the Second Temple after the Temple was destroyed. After the First Jewish-Roman war the tax was reworked to be more punitive. But the motive for using the tax against the Jews, in all forms, was explicitly for insurrection, not for religious/theological disputes.
The Roman state did understand how to violate Judaic practice and when Roman-Jewish relations were deteriorating, they used this intentional humiliation to exacerbate the issue. These intentional offenses included insertion of a Roman emperor's statue into the Jewish Temple and erection of altars inside other Jewish places of worship.
Here's an example of one of the proclamations guaranteeing Jewish freedom to practice:
Caesar Augustus, pontifex maximus, holding the tribunician power, proclaims: Since the nation of the Jews and Hyrcanus, their high priest, have been found grateful to the people of the Romans, not only in the present but also in the past, and particularly in the time of my father, Caesar, imperator, it seems good to me and to my advisory council, according to the oaths, by the will of the people of the Romans, that the Jews shall use their own customs in accordance with their ancestral law, just as they used to use them in the time of Hyrcanus, the high priest of their highest god; and that their sacred offerings shall be inviolable and shall be sent to Jerusalem and shall be paid to the financial officials of Jerusalem; and that they shall not give sureties for appearance in court on the Sabbath or on the day of preparation before it after the ninth hour. But if anyone is detected stealing their sacred books or their sacred monies, either from a synagogue or from a mens' apartment, he shall be considered sacrilegious and his property shall be brought into the public treasury of the Romans.
Translation from http://sourcebooks.fordham.edu/ancient/roman-jews.asp. On this site there's another edict from Claudius basically saying the same in less words.
Be sure to not assume that this tolerance for Judaism/monotheism extends forward past the early Principate. A lot of peoples' feelings got hurt and by the time Christianity was being perceived by the Roman state as a threat, the Genius of Caesar oaths were being used as tests to detect and impede monotheists.