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	$212.91	12.603%	$239.743	$239.74	$239.75	$239.70
Purchase #2	$155.94	10.492%	$172.3012	$172.30	$172.30	$172.30
Purchase #3	$222.67	8.652%	$241.9354	$241.94	$241.95	$241.90
Purchase #4	$35.97	13.600%	$40.8619	$40.86	$40.85	$40.90
Purchase #5	$201.57	7.545%	$216.7785	$216.78	$216.80	$216.80
Purchase #6	$128.45	12.448%	$144.4395	$144.44	$144.45	$144.40
Purchase #7	$215.73	3.146%	$222.5169	$222.52	$222.50	$222.50
7 purchase totals =	$1,173.24		$1,278.5764	$1,278.58	$1,278.60	$1,278.50