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	$228.55	12.228%	$256.4971	$256.50	$256.50	$256.50
Purchase #2	$52.40	6.538%	$55.8259	$55.83	$55.85	$55.80
Purchase #3	$9.52	6.106%	$10.1013	$10.10	$10.10	$10.10
Purchase #4	$48.67	7.730%	$52.4322	$52.43	$52.45	$52.40
Purchase #5	$202.37	10.205%	$223.0219	$223.02	$223.00	$223.00
Purchase #6	$215.45	10.363%	$237.7771	$237.78	$237.80	$237.80
Purchase #7	$58.26	10.831%	$64.5701	$64.57	$64.55	$64.60
7 purchase totals =	$815.22		$900.2256	$900.23	$900.25	$900.20