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	$21.62	5.366%	$22.7801	$22.78	$22.80	$22.80
Purchase #2	$17.34	3.802%	$17.9993	$18.00	$18.00	$18.00
Purchase #3	$158.46	4.438%	$165.4925	$165.49	$165.50	$165.50
Purchase #4	$80.32	12.735%	$90.5488	$90.55	$90.55	$90.50
Purchase #5	$205.65	8.756%	$223.6567	$223.66	$223.65	$223.70
Purchase #6	$95.94	6.721%	$102.3881	$102.39	$102.40	$102.40
Purchase #7	$192.98	3.493%	$199.7208	$199.72	$199.70	$199.70
7 purchase totals =	$772.31		$822.5863	$822.59	$822.60	$822.60