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	$193.54	12.121%	$216.999	$217.00	$217.00	$217.00
Purchase #2	$99.42	4.534%	$103.9277	$103.93	$103.95	$103.90
Purchase #3	$54.66	9.434%	$59.8166	$59.82	$59.80	$59.80
Purchase #4	$55.52	12.315%	$62.3573	$62.36	$62.35	$62.40
Purchase #5	$128.77	11.851%	$144.0305	$144.03	$144.05	$144.00
Purchase #6	$55.45	9.355%	$60.6373	$60.64	$60.65	$60.60
Purchase #7	$116.71	9.748%	$128.0869	$128.09	$128.10	$128.10
7 purchase totals =	$704.07		$775.8553	$775.87	$775.90	$775.80