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	$12.34	10.165%	$13.5944	$13.59	$13.60	$13.60
Purchase #2	$106.53	10.849%	$118.0874	$118.09	$118.10	$118.10
Purchase #3	$14.28	4.552%	$14.93	$14.93	$14.95	$14.90
Purchase #4	$103.81	6.597%	$110.6583	$110.66	$110.65	$110.70
Purchase #5	$39.76	6.870%	$42.4915	$42.49	$42.50	$42.50
Purchase #6	$154.93	6.782%	$165.4374	$165.44	$165.45	$165.40
Purchase #7	$69.49	13.142%	$78.6224	$78.62	$78.60	$78.60
7 purchase totals =	$501.14		$543.8214	$543.82	$543.85	$543.80