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	$23.35	7.438%	$25.0868	$25.09	$25.10	$25.10
Purchase #2	$233.35	8.783%	$253.8451	$253.85	$253.85	$253.80
Purchase #3	$20.90	4.826%	$21.9086	$21.91	$21.90	$21.90
Purchase #4	$153.51	12.464%	$172.6435	$172.64	$172.65	$172.60
Purchase #5	$52.84	12.759%	$59.5819	$59.58	$59.60	$59.60
Purchase #6	$213.95	9.168%	$233.5649	$233.56	$233.55	$233.60
Purchase #7	$120.77	3.343%	$124.8073	$124.81	$124.80	$124.80
7 purchase totals =	$818.67		$891.4381	$891.44	$891.45	$891.40