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	$16.93	8.788%	$18.4178	$18.42	$18.40	$18.40
Purchase #2	$35.76	3.837%	$37.1321	$37.13	$37.15	$37.10
Purchase #3	$171.66	10.766%	$190.1409	$190.14	$190.15	$190.10
Purchase #4	$124.40	5.661%	$131.4423	$131.44	$131.45	$131.40
Purchase #5	$143.27	10.637%	$158.5096	$158.51	$158.50	$158.50
Purchase #6	$121.97	13.495%	$138.4299	$138.43	$138.45	$138.40
Purchase #7	$76.67	6.509%	$81.6605	$81.66	$81.65	$81.70
7 purchase totals =	$690.66		$755.7331	$755.73	$755.75	$755.60