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	$206.80	13.168%	$234.0314	$234.03	$234.05	$234.00
Purchase #2	$249.47	10.140%	$274.7663	$274.77	$274.75	$274.80
Purchase #3	$205.69	13.313%	$233.0735	$233.07	$233.05	$233.10
Purchase #4	$166.69	3.738%	$172.9209	$172.92	$172.90	$172.90
Purchase #5	$32.43	12.240%	$36.3994	$36.40	$36.40	$36.40
Purchase #6	$48.64	12.642%	$54.7891	$54.79	$54.80	$54.80
Purchase #7	$68.46	12.624%	$77.1024	$77.10	$77.10	$77.10
7 purchase totals =	$978.18		$1,083.0830	$1,083.08	$1,083.05	$1,083.10