Wow, that's pretty messed up. I thought New York had a complicated sales tax system. I used to live in Texas for a little while, but I was a kid then, so I didn't have to deal with sales tax.

Anyhow, I would create separate fields for this on each record. You would need:

StateSalesTax
CountySalesTax
CitySalesTax
SpecialPurposeTax
TransitTax

Now, the State sales tax is 6.25% for NOW, but this could change. You'll then need a table where you can DLOOKUP the different taxes, which you say you already have built.

The last step, the TransitTax will be the hardest to figure out. I would say something like this in my VB code:

TaxTotal = [add up ALL the taxes here A+B+C+D+E]
If TaxTotal > 8.25 then
  Overage = TaxTotal - 8.25  ' how much are you over
  TransitTax = TransitTax - Overage  ' subtract overage from transit
End If

Of course, you might also want to check and make sure TransitTax isn't NEGATIVE at this point. In which case, you have to decide what to do.

Now update the TransitTax in your database. I would do all of this in an AfterUpdate event when you calculate your taxes per record.

Now generating your quarterly reports should be easy because you have all of the separate taxes stored in their own fields.