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	$99.67	4.129%	$103.7854	$103.79	$103.80	$103.80
Purchase #2	$97.57	8.207%	$105.5776	$105.58	$105.60	$105.60
Purchase #3	$188.27	5.549%	$198.7171	$198.72	$198.70	$198.70
Purchase #4	$145.83	13.370%	$165.3275	$165.33	$165.35	$165.30
Purchase #5	$60.84	9.144%	$66.4032	$66.40	$66.40	$66.40
Purchase #6	$167.57	3.490%	$173.4182	$173.42	$173.40	$173.40
Purchase #7	$74.85	11.415%	$83.3941	$83.39	$83.40	$83.40
7 purchase totals =	$834.60		$896.6231	$896.63	$896.65	$896.60