Don,
Hmm.. there's a lot of confusion about the NYS/NYC tax topic - at least in my mind. I think you may be wrong about there being no tax period regardless of cost.. Since i'm a pretty good programmer (but a rather poor accountant) I did some research and found this:
http://www.tax.state.ny.us/pdf/publications/sales/pub718c_807.pdf
Take a look at part 2, in particular this footnote to the NYC jurisdiction:
Effective September 1, 2007, sales in New York City of clothing and footwear, and items used to make or repair clothing, costing $110 or more per item or pair, are also exempt from the 4% New York City local tax. These sales remain subject to the New York State 4% sales and use tax and the ⅜% sales and use tax imposed by the state in the Metropolitan Commuter Transportation District.
The way I am reading this is that clothing and footwear that costs more than 110 dollars still has the 4.375% (combined) NYS and MCTD sales and use taxes. Conversely items under 110 are no subject to the state taxes. I might just call the 800 number they list and talk to someone there and get final confirmation that I am interpreting this correctly..
Anyway, thanks so much for your reply - i started poking around order.php and am getting familiarized with the system. I appreciate the offer of code snippets - i may take you up on your offer if I feel like i'm not getting anywhere but right now i'm kinda eager for the challenge. :P i'll happily share my code, too, once i write it after I get the final confirmation on what the business logic should be!