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	$44.75	13.560%	$50.8181	$50.82	$50.80	$50.80
Purchase #2	$137.47	13.184%	$155.594	$155.59	$155.60	$155.60
Purchase #3	$58.65	12.206%	$65.8088	$65.81	$65.80	$65.80
Purchase #4	$216.30	8.401%	$234.4714	$234.47	$234.45	$234.50
Purchase #5	$182.81	10.640%	$202.261	$202.26	$202.25	$202.30
Purchase #6	$66.83	6.131%	$70.9273	$70.93	$70.95	$70.90
Purchase #7	$81.75	10.456%	$90.2978	$90.30	$90.30	$90.30
7 purchase totals =	$788.56		$870.1784	$870.18	$870.15	$870.20