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	$239.40	7.179%	$256.5865	$256.59	$256.60	$256.60
Purchase #2	$181.35	5.167%	$190.7204	$190.72	$190.70	$190.70
Purchase #3	$63.87	4.438%	$66.7046	$66.70	$66.70	$66.70
Purchase #4	$8.92	13.644%	$10.137	$10.14	$10.15	$10.10
Purchase #5	$164.91	13.491%	$187.158	$187.16	$187.15	$187.20
Purchase #6	$71.55	4.198%	$74.5537	$74.55	$74.55	$74.60
Purchase #7	$37.82	11.361%	$42.1167	$42.12	$42.10	$42.10
7 purchase totals =	$767.82		$827.9769	$827.98	$827.95	$828.00