Aside from silly "sales-tax-holidays" I've never heard of the sales tax rates changing so frequently. I'm curious to know where this is happening "multiple times per year". Here in MA it's been the same rate for 15 years.
And for the sales-tax-holiday situation can't a shop just say something like "everything will have x% taken off at the register" just like they would during a typical "10% off all items" type of sale?