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	$106.30	5.657%	$112.3134	$112.31	$112.30	$112.30
Purchase #2	$118.89	7.373%	$127.6558	$127.66	$127.65	$127.70
Purchase #3	$226.51	12.749%	$255.3878	$255.39	$255.40	$255.40
Purchase #4	$42.34	13.468%	$48.0424	$48.04	$48.05	$48.00
Purchase #5	$30.64	12.201%	$34.3784	$34.38	$34.40	$34.40
Purchase #6	$148.52	11.154%	$165.0859	$165.09	$165.10	$165.10
Purchase #7	$178.98	5.195%	$188.278	$188.28	$188.30	$188.30
7 purchase totals =	$852.18		$931.1417	$931.15	$931.20	$931.20