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	$57.59	4.347%	$60.0934	$60.09	$60.10	$60.10
Purchase #2	$226.96	13.462%	$257.5134	$257.51	$257.50	$257.50
Purchase #3	$115.56	6.840%	$123.4643	$123.46	$123.45	$123.50
Purchase #4	$95.45	5.651%	$100.8439	$100.84	$100.85	$100.80
Purchase #5	$60.68	11.581%	$67.7074	$67.71	$67.70	$67.70
Purchase #6	$226.83	9.164%	$247.6167	$247.62	$247.60	$247.60
Purchase #7	$223.72	3.816%	$232.2572	$232.26	$232.25	$232.30
7 purchase totals =	$1,006.79		$1,089.4963	$1,089.49	$1,089.45	$1,089.50