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	$47.67	5.609%	$50.3438	$50.34	$50.35	$50.30
Purchase #2	$135.86	6.414%	$144.5741	$144.57	$144.55	$144.60
Purchase #3	$45.55	5.643%	$48.1204	$48.12	$48.10	$48.10
Purchase #4	$80.60	11.433%	$89.815	$89.82	$89.80	$89.80
Purchase #5	$52.42	11.670%	$58.5374	$58.54	$58.55	$58.50
Purchase #6	$9.81	13.690%	$11.153	$11.15	$11.15	$11.20
Purchase #7	$215.35	12.137%	$241.487	$241.49	$241.50	$241.50
7 purchase totals =	$587.26		$644.0307	$644.03	$644.00	$644.00