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	$17.35	4.623%	$18.1521	$18.15	$18.15	$18.20
Purchase #2	$16.38	4.693%	$17.1487	$17.15	$17.15	$17.10
Purchase #3	$177.61	10.726%	$196.6604	$196.66	$196.65	$196.70
Purchase #4	$97.58	6.507%	$103.9295	$103.93	$103.95	$103.90
Purchase #5	$29.76	9.453%	$32.5732	$32.57	$32.55	$32.60
Purchase #6	$237.62	13.528%	$269.7652	$269.77	$269.75	$269.80
Purchase #7	$155.59	11.725%	$173.8329	$173.83	$173.85	$173.80
7 purchase totals =	$731.89		$812.0620	$812.06	$812.05	$812.10