The community seems pretty dead..
sure, lots of people post their problems every day, but there are hardly anyone helping out with solutions :(
I did post some simple questions about two weeks ago regarding what files I could find the tax calculations for the cart and checkout.. not a soul answers.. and I seen alot more of these subjects where there is a question that should be rather simple to answer but it stays unanswered for 3 weeks or more.
I’m not exactly sure what your question is, but taxes are handled in admin panel-->Sales-->Tax-->…
My store is in LA, so I had to create a spreadsheet listing all LA zip codes, and 8.25% (or whatever it was) in the Rate1 column, and 0% in all the other rate columns. I also added a line with * as the zip (to catch all zips that didn’t match any I listed for LA) with 7.25% (or whatever it was) in the Rate1 column and 0 in all other rate columns. I imported this into the tax rates. (If you export one first, you’ll have a good example to start with. I used CSV and it worked fine for me. I’ve heard of problems importing other things using the XL format, so I didn’t bother with that.)
You then have to define customer types: mostly “Retail Customer” will be fine. And you have to define rules, for instance that a Retail Customer pays Rate 1. If you have some type of non-taxed customer, set up a rule that they pay Rate 2. If you need some other rate, add a Rate3 and create a customer type who gets that rate.
This should get you started.
Sorry if that didn’t address your question… it just occurred to me you probably meant which PHP file, not where’s the data file… in which case I have no idea. That would take some serious digging, and you might have to do that yourself and post back here where you found it.