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	$63.45	5.104%	$66.6885	$66.69	$66.70	$66.70
Purchase #2	$86.44	3.416%	$89.3928	$89.39	$89.40	$89.40
Purchase #3	$9.98	6.482%	$10.6269	$10.63	$10.65	$10.60
Purchase #4	$17.80	6.414%	$18.9417	$18.94	$18.95	$18.90
Purchase #5	$172.55	13.392%	$195.6579	$195.66	$195.65	$195.70
Purchase #6	$105.59	11.840%	$118.0919	$118.09	$118.10	$118.10
Purchase #7	$113.53	8.757%	$123.4718	$123.47	$123.45	$123.50
7 purchase totals =	$569.34		$622.8715	$622.87	$622.90	$622.90