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	$29.62	9.749%	$32.5077	$32.51	$32.50	$32.50
Purchase #2	$90.90	6.210%	$96.5449	$96.54	$96.55	$96.50
Purchase #3	$232.59	10.441%	$256.8747	$256.87	$256.85	$256.90
Purchase #4	$172.34	13.803%	$196.1281	$196.13	$196.15	$196.10
Purchase #5	$10.99	10.500%	$12.144	$12.14	$12.15	$12.10
Purchase #6	$44.66	8.436%	$48.4275	$48.43	$48.45	$48.40
Purchase #7	$20.52	11.723%	$22.9256	$22.93	$22.95	$22.90
7 purchase totals =	$601.62		$665.5525	$665.55	$665.60	$665.40