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	$59.82	10.493%	$66.0969	$66.10	$66.10	$66.10
Purchase #2	$153.32	8.178%	$165.8585	$165.86	$165.85	$165.90
Purchase #3	$172.55	10.363%	$190.4314	$190.43	$190.45	$190.40
Purchase #4	$179.26	11.654%	$200.151	$200.15	$200.15	$200.20
Purchase #5	$235.86	12.556%	$265.4746	$265.47	$265.45	$265.50
Purchase #6	$178.42	4.817%	$187.0145	$187.01	$187.00	$187.00
Purchase #7	$99.50	11.198%	$110.642	$110.64	$110.65	$110.60
7 purchase totals =	$1,078.73		$1,185.6689	$1,185.66	$1,185.65	$1,185.70