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	$58.69	12.394%	$65.964	$65.96	$65.95	$66.00
Purchase #2	$241.81	5.805%	$255.8471	$255.85	$255.85	$255.80
Purchase #3	$23.90	4.152%	$24.8923	$24.89	$24.90	$24.90
Purchase #4	$12.97	3.169%	$13.381	$13.38	$13.40	$13.40
Purchase #5	$176.27	8.692%	$191.5914	$191.59	$191.60	$191.60
Purchase #6	$105.41	7.826%	$113.6594	$113.66	$113.65	$113.70
Purchase #7	$140.71	10.183%	$155.0385	$155.04	$155.05	$155.00
7 purchase totals =	$759.76		$820.3737	$820.37	$820.40	$820.40