I shipped with UPS to US a few weeks ago and while it mentioned that there will be a tax at delivery it seems it was not.
I just asked the person I shipped a new SBMS0 + a repaired SBMS0 with UPS and he mentioned that he did not needed to pay anything. I declared it as made in Canada so maybe is under CUSMA and there are no taxes for this.
Maybe I will remove the shipping limitation to US next week and ship with UPS once every 10 days or so (not very convenient for me as I need to drive about 160km (100miles) to UPS) and see if there is consistently no tax.