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	$33.87	6.305%	$36.0055	$36.01	$36.00	$36.00
Purchase #2	$87.48	3.530%	$90.568	$90.57	$90.55	$90.60
Purchase #3	$152.78	3.509%	$158.1411	$158.14	$158.15	$158.10
Purchase #4	$23.36	10.106%	$25.7208	$25.72	$25.70	$25.70
Purchase #5	$59.61	3.123%	$61.4716	$61.47	$61.45	$61.50
Purchase #6	$149.95	11.456%	$167.1283	$167.13	$167.15	$167.10
Purchase #7	$137.43	10.456%	$151.7997	$151.80	$151.80	$151.80
7 purchase totals =	$644.48		$690.8350	$690.84	$690.80	$690.80