I seem to be having trouble with this as well. I just recently upgraded to 1.3.0.2 and have read and tried a lot of the mods posted in the forums about the tax rounding issue.

My site is http://staging.mindmint.s402.sureserver.com/

My state sales tax is 8.6%. I am using a dollars off coupon based on order total. I have read that ZenCart will add the tax amount to each line item or quantity on a line item, then sum everything together, and do the rest of the calculations specified in the Order Total hierarchy. Is there no fix or way around this? My order totals are off more than a penny like some people mention.

Also -- when I go to delete the Sales Tax config and create a new one, it confirms that I would like to delete 9% sales tax, not 8.6%. What gives there???

Example:
2 x Freedom From Maternal Depression (2 Compact Discs) $88.00
Sub-Total:
$88.00

Standard US Shipping (Standard Rate 5-7 Business Days):
$8.50

Discount Coupon: SAVE5 :
-$5.00

8.6% WA Sales Tax:
$7.57

Total:
$99.07

This should really total $44 + $44 + $8.50 - $5.00 * 1.086 = $99.37
NOT $44 * 1.086 + $44 * 1.086 + $8.50 - $5.00 = $99.07

If this can't be easily fixed then what? I'm in a situation where configuring ZC has take me nearly a year and I would hate to scrap this and return money on this job just because ZC doesn't follow basic mathematical rules. What gives?