Answer by Wray Rives:
First it is important to know that most of the sales tax holidays are limited in their application. The majority of the holidays are promoted as a "back to school" break and are timed to occur early to mid August and apply to things like clothing and in some other cases typical school type items.
- New Mexico
- S Carolina
All have some period where some otherwise taxable items are exempt from sales tax. See the blog post referenced in's answer for more specifics.
I would say that from a retailer's perspective sales tax holidays are more of a chance to get full retail price or defer price discounting due to the buying frenzy it can create. Reality is if you wait until the week after the sales tax holiday, you can very often save more than the 6-9% tax .