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	$46.25	5.318%	$48.7096	$48.71	$48.70	$48.70
Purchase #2	$194.82	5.188%	$204.9273	$204.93	$204.95	$204.90
Purchase #3	$56.42	11.360%	$62.8293	$62.83	$62.85	$62.80
Purchase #4	$227.86	12.476%	$256.2878	$256.29	$256.30	$256.30
Purchase #5	$91.56	9.251%	$100.0302	$100.03	$100.05	$100.00
Purchase #6	$140.43	10.293%	$154.8845	$154.88	$154.90	$154.90
Purchase #7	$178.55	3.301%	$184.4439	$184.44	$184.45	$184.40
7 purchase totals =	$935.89		$1,012.1126	$1,012.11	$1,012.20	$1,012.00