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	$5.90	13.552%	$6.6996	$6.70	$6.70	$6.70
Purchase #2	$32.83	8.828%	$35.7282	$35.73	$35.75	$35.70
Purchase #3	$87.74	3.504%	$90.8144	$90.81	$90.80	$90.80
Purchase #4	$198.34	12.166%	$222.47	$222.47	$222.45	$222.50
Purchase #5	$239.99	12.164%	$269.1824	$269.18	$269.20	$269.20
Purchase #6	$140.53	7.716%	$151.3733	$151.37	$151.35	$151.40
Purchase #7	$93.67	6.519%	$99.7763	$99.78	$99.80	$99.80
7 purchase totals =	$799.00		$876.0442	$876.04	$876.05	$876.10