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	$58.52	12.658%	$65.9275	$65.93	$65.95	$65.90
Purchase #2	$35.81	6.685%	$38.2039	$38.20	$38.20	$38.20
Purchase #3	$102.84	9.796%	$112.9142	$112.91	$112.90	$112.90
Purchase #4	$84.65	5.729%	$89.4996	$89.50	$89.50	$89.50
Purchase #5	$185.45	13.113%	$209.7681	$209.77	$209.75	$209.80
Purchase #6	$94.37	10.820%	$104.5808	$104.58	$104.60	$104.60
Purchase #7	$176.83	8.413%	$191.7067	$191.71	$191.70	$191.70
7 purchase totals =	$738.47		$812.6008	$812.60	$812.60	$812.60