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	$10.73	9.245%	$11.722	$11.72	$11.70	$11.70
Purchase #2	$43.96	12.231%	$49.3367	$49.34	$49.35	$49.30
Purchase #3	$13.70	6.149%	$14.5424	$14.54	$14.55	$14.50
Purchase #4	$173.41	11.226%	$192.877	$192.88	$192.90	$192.90
Purchase #5	$78.99	13.103%	$89.3401	$89.34	$89.35	$89.30
Purchase #6	$83.77	10.536%	$92.596	$92.60	$92.60	$92.60
Purchase #7	$37.69	10.523%	$41.6561	$41.66	$41.65	$41.70
7 purchase totals =	$442.25		$492.0703	$492.08	$492.10	$492.00