If you have variable "DynamicPermutationPricesTaxRate" set to 1.175 you'll have to change this.
The reason for this extra variable is that the default tax rate that Actinic uses isn’t available in a Variable (tut-tut Actinic).
My add on uses its own variable “DynamicPermutationPricesTaxRate”. Look in Design / Library / Variables (and use the Find Command to locate it).
It’s list of values so add a new value 1.15 and then select that as the default in Settings / Site Options / Layout / Site.