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	$38.72	3.692%	$40.1495	$40.15	$40.15	$40.10
Purchase #2	$12.83	9.327%	$14.0267	$14.03	$14.05	$14.00
Purchase #3	$34.66	13.545%	$39.3547	$39.35	$39.35	$39.40
Purchase #4	$13.60	6.301%	$14.4569	$14.46	$14.45	$14.50
Purchase #5	$227.53	6.628%	$242.6107	$242.61	$242.60	$242.60
Purchase #6	$168.69	9.781%	$185.1896	$185.19	$185.20	$185.20
Purchase #7	$81.78	12.241%	$91.7907	$91.79	$91.80	$91.80
7 purchase totals =	$577.81		$627.5788	$627.58	$627.60	$627.60