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	$16.51	11.768%	$18.4529	$18.45	$18.45	$18.50
Purchase #2	$95.33	11.373%	$106.1719	$106.17	$106.15	$106.20
Purchase #3	$100.63	11.812%	$112.5164	$112.52	$112.50	$112.50
Purchase #4	$154.97	11.491%	$172.7776	$172.78	$172.80	$172.80
Purchase #5	$184.85	3.247%	$190.8521	$190.85	$190.85	$190.90
Purchase #6	$150.90	5.138%	$158.6532	$158.65	$158.65	$158.70
Purchase #7	$39.91	9.832%	$43.834	$43.83	$43.85	$43.80
7 purchase totals =	$743.10		$803.2581	$803.25	$803.25	$803.40