Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
Case	Tag   Price	Sales   Tax %	Raw Total   Incl. Sales Tax	Rounded   to Penny	Rounded   to Nickel	Rounded   to Dime
Purchase #1	$159.53	12.566%	$179.5765	$179.58	$179.60	$179.60
Purchase #2	$159.98	8.279%	$173.2247	$173.22	$173.20	$173.20
Purchase #3	$86.31	10.695%	$95.5409	$95.54	$95.55	$95.50
Purchase #4	$177.82	4.196%	$185.2813	$185.28	$185.30	$185.30
Purchase #5	$90.56	13.810%	$103.0663	$103.07	$103.05	$103.10
Purchase #6	$60.99	13.715%	$69.3548	$69.35	$69.35	$69.40
Purchase #7	$50.29	8.644%	$54.6371	$54.64	$54.65	$54.60
7 purchase totals =	$785.48		$860.6816	$860.68	$860.70	$860.70