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	$130.40	6.688%	$139.1212	$139.12	$139.10	$139.10
Purchase #2	$146.44	13.162%	$165.7144	$165.71	$165.70	$165.70
Purchase #3	$139.48	8.315%	$151.0778	$151.08	$151.10	$151.10
Purchase #4	$174.77	9.111%	$190.6933	$190.69	$190.70	$190.70
Purchase #5	$193.58	13.567%	$219.843	$219.84	$219.85	$219.80
Purchase #6	$133.52	4.396%	$139.3895	$139.39	$139.40	$139.40
Purchase #7	$163.34	13.429%	$185.2749	$185.27	$185.25	$185.30
7 purchase totals =	$1,081.53		$1,191.1141	$1,191.10	$1,191.10	$1,191.10