Possible bug

I try a discount 100% for the shirt number 3, so the action is 3 shirt for 2, see my screenshot, the price of my cheapest shirt is 89€, but the discount is 90€, is this a bug?

also please i have a question, can you add in this plugin an option if I want use a promo code?

I think I found the problem.
Send me your TAX settings  (inc or excl TAX) and if you use 'ForceTaxExclusionFromOrderSubtotal'.
I'll calculate discount  for product with TAX... maybe we'll have a problem with rounding...

I think I'll add new parameter  'Requires coupon code'.