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	$212.38	12.463%	$238.8489	$238.85	$238.85	$238.80
Purchase #2	$132.31	11.796%	$147.9173	$147.92	$147.90	$147.90
Purchase #3	$238.39	7.492%	$256.2502	$256.25	$256.25	$256.30
Purchase #4	$12.31	9.548%	$13.4854	$13.49	$13.50	$13.50
Purchase #5	$11.73	8.789%	$12.7609	$12.76	$12.75	$12.80
Purchase #6	$74.61	9.648%	$81.8084	$81.81	$81.80	$81.80
Purchase #7	$112.50	10.337%	$124.1291	$124.13	$124.15	$124.10
7 purchase totals =	$794.23		$875.2002	$875.21	$875.20	$875.20