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	$9.26	13.762%	$10.5344	$10.53	$10.55	$10.50
Purchase #2	$171.61	4.750%	$179.7615	$179.76	$179.75	$179.80
Purchase #3	$165.55	4.378%	$172.7978	$172.80	$172.80	$172.80
Purchase #4	$118.40	4.557%	$123.7955	$123.80	$123.80	$123.80
Purchase #5	$161.52	9.245%	$176.4525	$176.45	$176.45	$176.50
Purchase #6	$33.57	6.823%	$35.8605	$35.86	$35.85	$35.90
Purchase #7	$12.89	6.576%	$13.7376	$13.74	$13.75	$13.70
7 purchase totals =	$672.80		$712.9398	$712.94	$712.95	$713.00