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	$17.83	12.628%	$20.0816	$20.08	$20.10	$20.10
Purchase #2	$218.67	10.620%	$241.8928	$241.89	$241.90	$241.90
Purchase #3	$76.42	4.613%	$79.9453	$79.95	$79.95	$79.90
Purchase #4	$100.51	7.550%	$108.0985	$108.10	$108.10	$108.10
Purchase #5	$62.76	4.433%	$65.5422	$65.54	$65.55	$65.50
Purchase #6	$152.28	8.787%	$165.6608	$165.66	$165.65	$165.70
Purchase #7	$208.49	6.758%	$222.5798	$222.58	$222.60	$222.60
7 purchase totals =	$836.96		$903.8010	$903.80	$903.85	$903.80