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	$63.81	11.562%	$71.1877	$71.19	$71.20	$71.20
Purchase #2	$100.71	11.679%	$112.4719	$112.47	$112.45	$112.50
Purchase #3	$175.42	11.451%	$195.5073	$195.51	$195.50	$195.50
Purchase #4	$151.99	11.291%	$169.1512	$169.15	$169.15	$169.20
Purchase #5	$171.51	13.322%	$194.3586	$194.36	$194.35	$194.40
Purchase #6	$71.70	6.548%	$76.3949	$76.39	$76.40	$76.40
Purchase #7	$71.75	9.188%	$78.3424	$78.34	$78.35	$78.30
7 purchase totals =	$806.89		$897.4140	$897.41	$897.40	$897.50