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	$99.50	7.122%	$106.5864	$106.59	$106.60	$106.60
Purchase #2	$240.27	6.836%	$256.6949	$256.69	$256.70	$256.70
Purchase #3	$12.45	4.272%	$12.9819	$12.98	$13.00	$13.00
Purchase #4	$231.97	6.683%	$247.4726	$247.47	$247.45	$247.50
Purchase #5	$20.56	3.603%	$21.3008	$21.30	$21.30	$21.30
Purchase #6	$207.72	7.399%	$223.0892	$223.09	$223.10	$223.10
Purchase #7	$49.90	6.831%	$53.3087	$53.31	$53.30	$53.30
7 purchase totals =	$862.37		$921.4345	$921.43	$921.45	$921.50