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	$189.54	13.851%	$215.7932	$215.79	$215.80	$215.80
Purchase #2	$9.55	4.843%	$10.0125	$10.01	$10.00	$10.00
Purchase #3	$116.66	8.735%	$126.8503	$126.85	$126.85	$126.90
Purchase #4	$105.66	4.852%	$110.7866	$110.79	$110.80	$110.80
Purchase #5	$64.28	3.693%	$66.6539	$66.65	$66.65	$66.70
Purchase #6	$57.89	3.503%	$59.9179	$59.92	$59.90	$59.90
Purchase #7	$188.70	11.782%	$210.9326	$210.93	$210.95	$210.90
7 purchase totals =	$732.28		$800.9470	$800.94	$800.95	$801.00