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	$15.65	12.258%	$17.5684	$17.57	$17.55	$17.60
Purchase #2	$18.96	13.503%	$21.5202	$21.52	$21.50	$21.50
Purchase #3	$26.74	11.604%	$29.8429	$29.84	$29.85	$29.80
Purchase #4	$234.59	7.103%	$251.2529	$251.25	$251.25	$251.30
Purchase #5	$66.39	3.672%	$68.8278	$68.83	$68.85	$68.80
Purchase #6	$99.34	4.841%	$104.149	$104.15	$104.15	$104.10
Purchase #7	$99.70	5.833%	$105.5155	$105.52	$105.50	$105.50
7 purchase totals =	$561.37		$598.6767	$598.68	$598.65	$598.60