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	$66.95	10.262%	$73.8204	$73.82	$73.80	$73.80
Purchase #2	$87.28	4.140%	$90.8934	$90.89	$90.90	$90.90
Purchase #3	$150.60	3.157%	$155.3544	$155.35	$155.35	$155.40
Purchase #4	$71.59	7.169%	$76.7223	$76.72	$76.70	$76.70
Purchase #5	$162.50	3.601%	$168.3516	$168.35	$168.35	$168.40
Purchase #6	$56.49	5.382%	$59.5303	$59.53	$59.55	$59.50
Purchase #7	$13.51	7.274%	$14.4927	$14.49	$14.50	$14.50
7 purchase totals =	$608.92		$639.1651	$639.15	$639.15	$639.20