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	$71.34	11.537%	$79.5705	$79.57	$79.55	$79.60
Purchase #2	$93.72	10.825%	$103.8652	$103.87	$103.85	$103.90
Purchase #3	$97.89	5.857%	$103.6234	$103.62	$103.60	$103.60
Purchase #4	$63.55	9.371%	$69.5053	$69.51	$69.50	$69.50
Purchase #5	$127.49	3.580%	$132.0541	$132.05	$132.05	$132.10
Purchase #6	$131.86	10.661%	$145.9176	$145.92	$145.90	$145.90
Purchase #7	$15.81	7.607%	$17.0127	$17.01	$17.00	$17.00
7 purchase totals =	$601.66		$651.5488	$651.55	$651.45	$651.60