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	$158.57	8.837%	$172.5828	$172.58	$172.60	$172.60
Purchase #2	$40.76	12.427%	$45.8252	$45.83	$45.85	$45.80
Purchase #3	$237.68	13.662%	$270.1518	$270.15	$270.15	$270.20
Purchase #4	$181.58	4.528%	$189.8019	$189.80	$189.80	$189.80
Purchase #5	$229.71	4.852%	$240.8555	$240.86	$240.85	$240.90
Purchase #6	$9.66	4.671%	$10.1112	$10.11	$10.10	$10.10
Purchase #7	$28.56	4.208%	$29.7618	$29.76	$29.75	$29.80
7 purchase totals =	$886.52		$959.0902	$959.09	$959.10	$959.20