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	$18.59	10.868%	$20.6104	$20.61	$20.60	$20.60
Purchase #2	$78.58	7.184%	$84.2252	$84.23	$84.25	$84.20
Purchase #3	$53.66	5.485%	$56.6033	$56.60	$56.60	$56.60
Purchase #4	$132.61	6.681%	$141.4697	$141.47	$141.45	$141.50
Purchase #5	$111.75	10.157%	$123.1004	$123.10	$123.10	$123.10
Purchase #6	$63.35	3.462%	$65.5432	$65.54	$65.55	$65.50
Purchase #7	$39.98	5.665%	$42.2449	$42.24	$42.25	$42.20
7 purchase totals =	$498.52		$533.7971	$533.79	$533.80	$533.70