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	$7.56	3.490%	$7.8238	$7.82	$7.80	$7.80
Purchase #2	$140.42	10.531%	$155.2076	$155.21	$155.20	$155.20
Purchase #3	$82.64	6.427%	$87.9513	$87.95	$87.95	$88.00
Purchase #4	$18.89	11.492%	$21.0608	$21.06	$21.05	$21.10
Purchase #5	$206.88	7.639%	$222.6836	$222.68	$222.70	$222.70
Purchase #6	$85.50	5.103%	$89.8631	$89.86	$89.85	$89.90
Purchase #7	$29.93	12.153%	$33.5674	$33.57	$33.55	$33.60
7 purchase totals =	$571.82		$618.1576	$618.15	$618.10	$618.30