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	$199.47	11.640%	$222.6883	$222.69	$222.70	$222.70
Purchase #2	$141.43	6.703%	$150.9101	$150.91	$150.90	$150.90
Purchase #3	$155.54	3.868%	$161.5563	$161.56	$161.55	$161.60
Purchase #4	$89.71	12.375%	$100.8116	$100.81	$100.80	$100.80
Purchase #5	$143.82	4.246%	$149.9266	$149.93	$149.95	$149.90
Purchase #6	$73.45	12.707%	$82.7833	$82.78	$82.80	$82.80
Purchase #7	$245.93	13.110%	$278.1714	$278.17	$278.15	$278.20
7 purchase totals =	$1,049.35		$1,146.8476	$1,146.85	$1,146.85	$1,146.90