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	$19.52	8.463%	$21.172	$21.17	$21.15	$21.20
Purchase #2	$175.43	12.149%	$196.743	$196.74	$196.75	$196.70
Purchase #3	$79.48	13.727%	$90.3902	$90.39	$90.40	$90.40
Purchase #4	$241.78	4.391%	$252.3966	$252.40	$252.40	$252.40
Purchase #5	$88.94	12.745%	$100.2754	$100.28	$100.30	$100.30
Purchase #6	$199.84	13.268%	$226.3548	$226.35	$226.35	$226.40
Purchase #7	$9.92	12.406%	$11.1507	$11.15	$11.15	$11.20
7 purchase totals =	$814.91		$898.4827	$898.48	$898.50	$898.60