My guess is that the comment means there is always some minor tweaks to tax laws, so that tax on certain products could change, and that may happen a few times

My guess is that the comment means there is always some minor tweaks to tax laws, so that tax on certain products could change, and that may happen a few times a year. I don't think it means sales tax rate changes on all products a few times a year. There is a caveat -- if you count the "sales tax holidays" in various US states, it means in those places, tax rates for some products change at least twice a year -- from 7% to 0% then back to 7%, for example.