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	$18.91	10.734%	$20.9398	$20.94	$20.95	$20.90
Purchase #2	$147.35	6.504%	$156.9336	$156.93	$156.95	$156.90
Purchase #3	$11.39	3.847%	$11.8282	$11.83	$11.85	$11.80
Purchase #4	$6.92	7.722%	$7.4544	$7.45	$7.45	$7.50
Purchase #5	$178.78	6.373%	$190.1736	$190.17	$190.15	$190.20
Purchase #6	$24.57	10.425%	$27.1314	$27.13	$27.15	$27.10
Purchase #7	$108.94	7.246%	$116.8338	$116.83	$116.85	$116.80
7 purchase totals =	$496.86		$531.2948	$531.28	$531.35	$531.20