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	$47.54	3.360%	$49.1373	$49.14	$49.15	$49.10
Purchase #2	$225.81	5.788%	$238.8799	$238.88	$238.90	$238.90
Purchase #3	$231.57	4.537%	$242.0763	$242.08	$242.10	$242.10
Purchase #4	$19.98	7.314%	$21.4413	$21.44	$21.45	$21.40
Purchase #5	$46.81	6.840%	$50.0118	$50.01	$50.00	$50.00
Purchase #6	$162.63	6.519%	$173.2318	$173.23	$173.25	$173.20
Purchase #7	$158.29	9.224%	$172.8907	$172.89	$172.90	$172.90
7 purchase totals =	$892.63		$947.6691	$947.67	$947.75	$947.60