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	$94.54	13.680%	$107.4731	$107.47	$107.45	$107.50
Purchase #2	$208.57	4.420%	$217.7888	$217.79	$217.80	$217.80
Purchase #3	$121.44	8.834%	$132.168	$132.17	$132.15	$132.20
Purchase #4	$116.81	9.161%	$127.511	$127.51	$127.50	$127.50
Purchase #5	$246.83	7.196%	$264.5919	$264.59	$264.60	$264.60
Purchase #6	$15.26	4.314%	$15.9183	$15.92	$15.90	$15.90
Purchase #7	$56.85	10.298%	$62.7044	$62.70	$62.70	$62.70
7 purchase totals =	$860.30		$928.1555	$928.15	$928.10	$928.20