This one could be long winded

and probably in the wrong section but I'm looking for suggestions on the best way to bring sales tax into our system.
After reading the March issue on the Invoice System, I decided to implement some of Tom's ideas into our point of sales system, which has brought about some other problems.
In our point of sale invoice system (which is not fully tested until we recieve the 1.0.2 upgrade for subform calculations) I have been working on bringing in the new State Sales Tax tables which went into effect the first of the year but we have till May to have it fully operational before we are in non-compliance.
Under this system we have to collect sales tax at the point of delivery which apparently is to work off the 5 digit zip code with the plus 4 to obtain the tax rate for that paticular address.
As this system now gives us over 872 tax rates for the state the question now comes to the best way to incorporate this into our invoice form.
With one or two tax rates it was easier to add it as a line item in the subform but with 872+ rates I placed a check box for taxable, an LE for tax after the subtotal and planned on doing a xlookup to return the tax rate then do the calculations.
As the State Dept of Revenue now tells us the downloadable date base will not be available until May and they don't know what format it will be in yet

but they tell us there is a data base on the Dept of Revenue's Website you can input the address to get the tax rate, or input the address invoice amount and it will return the tax amount.
I then get to thinking about the size of this database for these new tax codes; as it is to work off the zip +4 then every address for the state will be listed in it which will be around 3 to 5 million or better, so now what.
Is it possible to do a lookup to the website database in this scenario?
How taxing (excuse the pun) will this db and lookup be to Sesame if it were download into Sesame for use?
I also understand there is 13 states that have now introduced this tax system with more to follow, so if theres other Sesame users fighting this same problem I would like to hear how your handling it.
Or if you undeclared guru's of Sesame have any thoughts as to the best way to handle this to keep the burden to the system at a minimum, would love to hear it.
Ok, everyone reading this is now asking why is the state doing that, well it appears our governor thinks she going to start collecting sales tax from internet sales and this is stage one being implemented, talk about re-inventing the wheel