Subtotal + tax − discount.
Subtotal minus discount, plus tax on the discounted amount = grand total.
Standard invoice math.
Getting the discount-then-tax order right matters for the final number — applying tax before the discount instead of after produces a different (and incorrect) total, which is a surprisingly common invoicing mistake.
$1,000 subtotal, 8% tax, 0 discount = $1,000 × 1.08 = $1,080.00.
Standard is tax on the post-discount amount. Confirm your jurisdiction's rules.
Depends on state — many US states tax shipping if it's not separately stated as a distinct fee.
Rounding only the final total is generally more accurate and standard practice — rounding every individual line first can compound small errors across a multi-item invoice.