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	$77.45	7.717%	$83.4268	$83.43	$83.45	$83.40
Purchase #2	$198.87	11.274%	$221.2906	$221.29	$221.30	$221.30
Purchase #3	$249.83	10.294%	$275.5475	$275.55	$275.55	$275.50
Purchase #4	$92.28	13.123%	$104.3899	$104.39	$104.40	$104.40
Purchase #5	$37.27	6.758%	$39.7887	$39.79	$39.80	$39.80
Purchase #6	$56.38	6.660%	$60.1349	$60.13	$60.15	$60.10
Purchase #7	$223.32	6.176%	$237.1122	$237.11	$237.10	$237.10
7 purchase totals =	$935.40		$1,021.6906	$1,021.69	$1,021.75	$1,021.60