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	$18.49	11.761%	$20.6646	$20.66	$20.65	$20.70
Purchase #2	$64.55	4.724%	$67.5993	$67.60	$67.60	$67.60
Purchase #3	$47.59	11.197%	$52.9187	$52.92	$52.90	$52.90
Purchase #4	$134.46	5.404%	$141.7262	$141.73	$141.75	$141.70
Purchase #5	$153.94	8.217%	$166.5892	$166.59	$166.60	$166.60
Purchase #6	$158.60	7.542%	$170.5616	$170.56	$170.55	$170.60
Purchase #7	$57.40	5.453%	$60.53	$60.53	$60.55	$60.50
7 purchase totals =	$635.03		$680.5896	$680.59	$680.60	$680.60