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	$153.83	12.867%	$173.6233	$173.62	$173.60	$173.60
Purchase #2	$79.67	12.197%	$89.3873	$89.39	$89.40	$89.40
Purchase #3	$191.65	11.509%	$213.707	$213.71	$213.70	$213.70
Purchase #4	$11.28	6.449%	$12.0074	$12.01	$12.00	$12.00
Purchase #5	$238.66	11.111%	$265.1775	$265.18	$265.20	$265.20
Purchase #6	$156.66	11.799%	$175.1443	$175.14	$175.15	$175.10
Purchase #7	$59.75	3.820%	$62.0325	$62.03	$62.05	$62.00
7 purchase totals =	$891.50		$991.0793	$991.08	$991.10	$991.00