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	$10.41	10.501%	$11.5032	$11.50	$11.50	$11.50
Purchase #2	$120.41	9.390%	$131.7165	$131.72	$131.70	$131.70
Purchase #3	$221.64	10.459%	$244.8213	$244.82	$244.80	$244.80
Purchase #4	$243.38	10.748%	$269.5385	$269.54	$269.55	$269.50
Purchase #5	$8.50	11.732%	$9.4972	$9.50	$9.50	$9.50
Purchase #6	$108.78	5.629%	$114.9032	$114.90	$114.90	$114.90
Purchase #7	$140.79	7.381%	$151.1817	$151.18	$151.20	$151.20
7 purchase totals =	$853.91		$933.1616	$933.16	$933.15	$933.10