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	$224.57	6.175%	$238.4372	$238.44	$238.45	$238.40
Purchase #2	$73.87	13.205%	$83.6245	$83.62	$83.60	$83.60
Purchase #3	$122.61	4.745%	$128.4278	$128.43	$128.45	$128.40
Purchase #4	$173.70	5.625%	$183.4706	$183.47	$183.45	$183.50
Purchase #5	$130.84	6.334%	$139.1274	$139.13	$139.15	$139.10
Purchase #6	$65.34	5.171%	$68.7187	$68.72	$68.70	$68.70
Purchase #7	$126.27	8.618%	$137.1519	$137.15	$137.15	$137.20
7 purchase totals =	$917.20		$978.9581	$978.96	$978.95	$978.90