Coupon checkout total error

When applying a discount coupon I am getting an error in the checkout total.

Cart contains 11 items.
Total pre coupon price is 390.00
Zen v1.3.6
discount coupon = 50%

Step 2 of checkout:
sub total 390.00
store pickup 0.00
tax (7.25%) 28.30
total 418.30

Step 3 of checkout:
sub total 390.00
store oickup 0.00
Discount coupon 195.00
total 67.21

The final total is grossly wrong. The sales tax calculation is overcharge by .02 as well.

Do I have some settings set wrong somewhere to correctly use the coupons?

Do you have a list of the 11 Product Prices and Quantities?

Ajeh:

Do you have a list of the 11 Product Prices and Quantities?

2-10.00
1-50.00
4-20.00
1-10.00
2-25.00
1-35.00
1-35.00
1-25.00
1.15.00
1-20.00
1-50.00

I think I may have caused a problem by having the customer with a group discount and then the customer also uses a discount coupon.
I guess you can't use both "group discount" and "discount coupon" at the same time??

I am trying to give a discount to wholesale customers and also discount state tax. I had assigned a group discount to discount the tax and then created a "discount coupon" for the 50%. I think the include tax and recalculate tax options might have conflicted with each other.

I solved the problem by making the group discount 57.25%.

Is there a tax exempt option?

Thanks for your help!