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	$63.47	5.788%	$67.1436	$67.14	$67.15	$67.10
Purchase #2	$111.83	5.457%	$117.9326	$117.93	$117.95	$117.90
Purchase #3	$30.28	7.452%	$32.5365	$32.54	$32.55	$32.50
Purchase #4	$18.83	6.509%	$20.0556	$20.06	$20.05	$20.10
Purchase #5	$231.32	3.236%	$238.8055	$238.81	$238.80	$238.80
Purchase #6	$175.46	5.223%	$184.6243	$184.62	$184.60	$184.60
Purchase #7	$78.82	3.275%	$81.4014	$81.40	$81.40	$81.40
7 purchase totals =	$710.01		$742.4995	$742.50	$742.50	$742.40