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	$55.49	9.514%	$60.7693	$60.77	$60.75	$60.80
Purchase #2	$233.92	11.318%	$260.3951	$260.40	$260.40	$260.40
Purchase #3	$229.31	5.723%	$242.4334	$242.43	$242.45	$242.40
Purchase #4	$207.70	12.533%	$233.731	$233.73	$233.75	$233.70
Purchase #5	$249.52	11.780%	$278.9135	$278.91	$278.90	$278.90
Purchase #6	$100.89	10.307%	$111.2887	$111.29	$111.30	$111.30
Purchase #7	$21.84	11.410%	$24.3319	$24.33	$24.35	$24.30
7 purchase totals =	$1,098.67		$1,211.8629	$1,211.86	$1,211.90	$1,211.80