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	$29.45	4.141%	$30.6695	$30.67	$30.65	$30.70
Purchase #2	$28.48	5.434%	$30.0276	$30.03	$30.05	$30.00
Purchase #3	$212.87	10.851%	$235.9685	$235.97	$235.95	$236.00
Purchase #4	$53.39	7.855%	$57.5838	$57.58	$57.60	$57.60
Purchase #5	$68.75	5.519%	$72.5443	$72.54	$72.55	$72.50
Purchase #6	$178.51	10.294%	$196.8858	$196.89	$196.90	$196.90
Purchase #7	$14.82	5.584%	$15.6475	$15.65	$15.65	$15.60
7 purchase totals =	$586.27		$639.3270	$639.33	$639.35	$639.30