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	$36.64	9.510%	$40.1245	$40.12	$40.10	$40.10
Purchase #2	$134.98	13.827%	$153.6437	$153.64	$153.65	$153.60
Purchase #3	$9.94	13.579%	$11.2898	$11.29	$11.30	$11.30
Purchase #4	$53.49	10.379%	$59.0417	$59.04	$59.05	$59.00
Purchase #5	$215.86	5.861%	$228.5116	$228.51	$228.50	$228.50
Purchase #6	$241.55	12.417%	$271.5433	$271.54	$271.55	$271.50
Purchase #7	$71.79	11.130%	$79.7802	$79.78	$79.80	$79.80
7 purchase totals =	$764.25		$843.9348	$843.92	$843.95	$843.80