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	$9.52	13.730%	$10.8271	$10.83	$10.85	$10.80
Purchase #2	$231.55	10.828%	$256.6222	$256.62	$256.60	$256.60
Purchase #3	$238.34	8.237%	$257.9721	$257.97	$257.95	$258.00
Purchase #4	$7.80	10.145%	$8.5913	$8.59	$8.60	$8.60
Purchase #5	$37.93	3.793%	$39.3687	$39.37	$39.35	$39.40
Purchase #6	$57.44	7.154%	$61.5493	$61.55	$61.55	$61.50
Purchase #7	$54.82	3.231%	$56.5912	$56.59	$56.60	$56.60
7 purchase totals =	$637.40		$691.5219	$691.52	$691.50	$691.50