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	$45.96	7.265%	$49.299	$49.30	$49.30	$49.30
Purchase #2	$144.86	3.793%	$150.3545	$150.35	$150.35	$150.40
Purchase #3	$173.54	7.104%	$185.8683	$185.87	$185.85	$185.90
Purchase #4	$230.76	9.321%	$252.2691	$252.27	$252.25	$252.30
Purchase #5	$99.59	13.841%	$113.3743	$113.37	$113.35	$113.40
Purchase #6	$247.72	11.235%	$275.5513	$275.55	$275.55	$275.60
Purchase #7	$143.54	8.345%	$155.5184	$155.52	$155.50	$155.50
7 purchase totals =	$1,085.97		$1,182.2349	$1,182.23	$1,182.15	$1,182.40