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	$221.27	8.317%	$239.673	$239.67	$239.65	$239.70
Purchase #2	$37.86	5.725%	$40.0275	$40.03	$40.05	$40.00
Purchase #3	$103.78	13.665%	$117.9615	$117.96	$117.95	$118.00
Purchase #4	$53.47	11.693%	$59.7222	$59.72	$59.70	$59.70
Purchase #5	$7.55	4.166%	$7.8645	$7.86	$7.85	$7.90
Purchase #6	$96.37	10.782%	$106.7606	$106.76	$106.75	$106.80
Purchase #7	$139.47	8.622%	$151.4951	$151.50	$151.50	$151.50
7 purchase totals =	$659.77		$723.5044	$723.50	$723.45	$723.60