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	$25.35	11.123%	$28.1697	$28.17	$28.15	$28.20
Purchase #2	$83.89	9.210%	$91.6163	$91.62	$91.60	$91.60
Purchase #3	$158.95	7.277%	$170.5168	$170.52	$170.50	$170.50
Purchase #4	$139.33	6.472%	$148.3474	$148.35	$148.35	$148.30
Purchase #5	$216.53	7.643%	$233.0794	$233.08	$233.10	$233.10
Purchase #6	$228.32	12.380%	$256.586	$256.59	$256.60	$256.60
Purchase #7	$127.67	10.538%	$141.1239	$141.12	$141.10	$141.10
7 purchase totals =	$980.04		$1,069.4395	$1,069.45	$1,069.40	$1,069.40