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	$58.63	13.486%	$66.5368	$66.54	$66.55	$66.50
Purchase #2	$42.54	3.867%	$44.185	$44.19	$44.20	$44.20
Purchase #3	$56.35	10.210%	$62.1033	$62.10	$62.10	$62.10
Purchase #4	$11.61	10.602%	$12.8409	$12.84	$12.85	$12.80
Purchase #5	$101.95	9.325%	$111.4568	$111.46	$111.45	$111.50
Purchase #6	$37.32	10.701%	$41.3136	$41.31	$41.30	$41.30
Purchase #7	$131.37	9.297%	$143.5835	$143.58	$143.60	$143.60
7 purchase totals =	$439.77		$482.0199	$482.02	$482.05	$482.00