Cities can pass conflicting legislation. It takes a court ruling to rule that it is, in fact, conflicting and kill it (and/or a judge to grant an injunction to stop it in the meantime).

San Francisco banned handguns decades ago. That was eventually ruled invalid because of state preemption, but SF had made its Grand Political Statement. CA taxpayers paid the legal costs. Yay.

Generally, taxes can't be challenged until they are actually collected (one famous example: Obamacare).