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	$117.43	8.421%	$127.3188	$127.32	$127.30	$127.30
Purchase #2	$29.89	8.363%	$32.3897	$32.39	$32.40	$32.40
Purchase #3	$235.84	12.446%	$265.1926	$265.19	$265.20	$265.20
Purchase #4	$61.30	6.802%	$65.4696	$65.47	$65.45	$65.50
Purchase #5	$94.74	11.227%	$105.3765	$105.38	$105.40	$105.40
Purchase #6	$234.62	7.820%	$252.9673	$252.97	$252.95	$253.00
Purchase #7	$233.30	7.867%	$251.6537	$251.65	$251.65	$251.70
7 purchase totals =	$1,007.12		$1,100.3682	$1,100.37	$1,100.35	$1,100.50