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	$55.29	10.496%	$61.0932	$61.09	$61.10	$61.10
Purchase #2	$108.45	5.845%	$114.7889	$114.79	$114.80	$114.80
Purchase #3	$52.62	8.807%	$57.2542	$57.25	$57.25	$57.30
Purchase #4	$24.94	12.327%	$28.0144	$28.01	$28.00	$28.00
Purchase #5	$212.61	5.163%	$223.5871	$223.59	$223.60	$223.60
Purchase #6	$72.83	11.142%	$80.9447	$80.94	$80.95	$80.90
Purchase #7	$20.72	3.109%	$21.3642	$21.36	$21.35	$21.40
7 purchase totals =	$547.46		$587.0467	$587.03	$587.05	$587.10