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	$225.78	13.352%	$255.9261	$255.93	$255.95	$255.90
Purchase #2	$46.50	11.654%	$51.9191	$51.92	$51.90	$51.90
Purchase #3	$117.48	4.678%	$122.9757	$122.98	$123.00	$123.00
Purchase #4	$184.42	3.843%	$191.5073	$191.51	$191.50	$191.50
Purchase #5	$18.89	11.337%	$21.0316	$21.03	$21.05	$21.00
Purchase #6	$67.89	3.853%	$70.5058	$70.51	$70.50	$70.50
Purchase #7	$143.56	10.576%	$158.7429	$158.74	$158.75	$158.70
7 purchase totals =	$804.52		$872.6085	$872.62	$872.65	$872.50