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	$74.60	10.369%	$82.3353	$82.34	$82.35	$82.30
Purchase #2	$89.77	7.116%	$96.158	$96.16	$96.15	$96.20
Purchase #3	$44.76	6.166%	$47.5199	$47.52	$47.50	$47.50
Purchase #4	$190.50	13.327%	$215.8879	$215.89	$215.90	$215.90
Purchase #5	$60.40	5.491%	$63.7166	$63.72	$63.70	$63.70
Purchase #6	$10.67	6.568%	$11.3708	$11.37	$11.35	$11.40
Purchase #7	$79.57	11.552%	$88.7619	$88.76	$88.75	$88.80
7 purchase totals =	$550.27		$605.7504	$605.76	$605.70	$605.80