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	$15.64	5.686%	$16.5293	$16.53	$16.55	$16.50
Purchase #2	$237.49	11.453%	$264.6897	$264.69	$264.70	$264.70
Purchase #3	$58.48	10.380%	$64.5502	$64.55	$64.55	$64.60
Purchase #4	$9.59	13.383%	$10.8734	$10.87	$10.85	$10.90
Purchase #5	$53.52	10.319%	$59.0427	$59.04	$59.05	$59.00
Purchase #6	$225.50	13.559%	$256.0755	$256.08	$256.10	$256.10
Purchase #7	$51.28	8.600%	$55.6901	$55.69	$55.70	$55.70
7 purchase totals =	$651.50		$727.4509	$727.45	$727.50	$727.50