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	$134.89	6.620%	$143.8197	$143.82	$143.80	$143.80
Purchase #2	$69.41	6.518%	$73.9341	$73.93	$73.95	$73.90
Purchase #3	$20.45	6.818%	$21.8443	$21.84	$21.85	$21.80
Purchase #4	$36.49	10.384%	$40.2791	$40.28	$40.30	$40.30
Purchase #5	$127.44	13.553%	$144.7119	$144.71	$144.70	$144.70
Purchase #6	$157.82	9.132%	$172.2321	$172.23	$172.25	$172.20
Purchase #7	$45.67	6.198%	$48.5006	$48.50	$48.50	$48.50
7 purchase totals =	$592.17		$645.3218	$645.31	$645.35	$645.20