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	$108.98	13.160%	$123.3218	$123.32	$123.30	$123.30
Purchase #2	$53.99	10.847%	$59.8463	$59.85	$59.85	$59.80
Purchase #3	$202.60	13.821%	$230.6013	$230.60	$230.60	$230.60
Purchase #4	$58.86	3.316%	$60.8118	$60.81	$60.80	$60.80
Purchase #5	$111.98	10.547%	$123.7905	$123.79	$123.80	$123.80
Purchase #6	$60.38	6.716%	$64.4351	$64.44	$64.45	$64.40
Purchase #7	$227.81	3.512%	$235.8107	$235.81	$235.80	$235.80
7 purchase totals =	$824.60		$898.6175	$898.62	$898.60	$898.50