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	$26.35	4.259%	$27.4722	$27.47	$27.45	$27.50
Purchase #2	$227.58	11.855%	$254.5596	$254.56	$254.55	$254.60
Purchase #3	$129.51	10.637%	$143.286	$143.29	$143.30	$143.30
Purchase #4	$198.67	3.232%	$205.091	$205.09	$205.10	$205.10
Purchase #5	$73.96	4.806%	$77.5145	$77.51	$77.50	$77.50
Purchase #6	$27.85	7.528%	$29.9465	$29.95	$29.95	$29.90
Purchase #7	$91.56	10.196%	$100.8955	$100.90	$100.90	$100.90
7 purchase totals =	$775.48		$838.7653	$838.77	$838.75	$838.80