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	$111.81	11.629%	$124.8124	$124.81	$124.80	$124.80
Purchase #2	$192.61	4.114%	$200.534	$200.53	$200.55	$200.50
Purchase #3	$16.32	8.610%	$17.7252	$17.73	$17.75	$17.70
Purchase #4	$191.43	9.500%	$209.6159	$209.62	$209.60	$209.60
Purchase #5	$56.73	8.376%	$61.4817	$61.48	$61.50	$61.50
Purchase #6	$83.98	13.430%	$95.2585	$95.26	$95.25	$95.30
Purchase #7	$28.64	10.273%	$31.5822	$31.58	$31.60	$31.60
7 purchase totals =	$681.52		$741.0099	$741.01	$741.05	$741.00