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	$151.59	4.568%	$158.5146	$158.51	$158.50	$158.50
Purchase #2	$24.86	8.763%	$27.0385	$27.04	$27.05	$27.00
Purchase #3	$236.27	13.720%	$268.6862	$268.69	$268.70	$268.70
Purchase #4	$211.80	10.341%	$233.7022	$233.70	$233.70	$233.70
Purchase #5	$82.99	10.699%	$91.8691	$91.87	$91.85	$91.90
Purchase #6	$223.86	7.843%	$241.4173	$241.42	$241.40	$241.40
Purchase #7	$70.45	12.140%	$79.0026	$79.00	$79.00	$79.00
7 purchase totals =	$1,001.82		$1,100.2305	$1,100.23	$1,100.20	$1,100.20