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	$15.93	10.365%	$17.5811	$17.58	$17.60	$17.60
Purchase #2	$158.28	5.684%	$167.2766	$167.28	$167.30	$167.30
Purchase #3	$84.58	5.549%	$89.2733	$89.27	$89.25	$89.30
Purchase #4	$143.33	13.456%	$162.6165	$162.62	$162.60	$162.60
Purchase #5	$75.62	10.509%	$83.5669	$83.57	$83.55	$83.60
Purchase #6	$246.28	8.726%	$267.7704	$267.77	$267.75	$267.80
Purchase #7	$175.48	11.801%	$196.1884	$196.19	$196.20	$196.20
7 purchase totals =	$899.50		$984.2732	$984.28	$984.25	$984.40