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	$131.37	4.581%	$137.3881	$137.39	$137.40	$137.40
Purchase #2	$137.68	11.291%	$153.2254	$153.23	$153.25	$153.20
Purchase #3	$100.62	10.862%	$111.5493	$111.55	$111.55	$111.50
Purchase #4	$192.37	6.176%	$204.2508	$204.25	$204.25	$204.30
Purchase #5	$12.93	7.132%	$13.8522	$13.85	$13.85	$13.90
Purchase #6	$92.62	8.139%	$100.1583	$100.16	$100.15	$100.20
Purchase #7	$244.32	5.427%	$257.5792	$257.58	$257.60	$257.60
7 purchase totals =	$911.91		$978.0033	$978.01	$978.05	$978.10