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	$58.75	13.213%	$66.5126	$66.51	$66.50	$66.50
Purchase #2	$246.37	6.569%	$262.554	$262.55	$262.55	$262.60
Purchase #3	$37.82	10.568%	$41.8168	$41.82	$41.80	$41.80
Purchase #4	$112.83	3.196%	$116.436	$116.44	$116.45	$116.40
Purchase #5	$25.60	3.792%	$26.5708	$26.57	$26.55	$26.60
Purchase #6	$27.89	4.474%	$29.1378	$29.14	$29.15	$29.10
Purchase #7	$17.33	6.169%	$18.3991	$18.40	$18.40	$18.40
7 purchase totals =	$526.59		$561.4271	$561.43	$561.40	$561.40