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	$231.65	9.391%	$253.4043	$253.40	$253.40	$253.40
Purchase #2	$126.69	12.424%	$142.43	$142.43	$142.45	$142.40
Purchase #3	$58.53	13.599%	$66.4895	$66.49	$66.50	$66.50
Purchase #4	$138.79	4.491%	$145.0231	$145.02	$145.00	$145.00
Purchase #5	$41.82	11.340%	$46.5624	$46.56	$46.55	$46.60
Purchase #6	$146.27	3.635%	$151.5869	$151.59	$151.60	$151.60
Purchase #7	$18.72	10.416%	$20.6699	$20.67	$20.65	$20.70
7 purchase totals =	$762.47		$826.1661	$826.16	$826.15	$826.20