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	$20.64	5.233%	$21.7201	$21.72	$21.70	$21.70
Purchase #2	$202.79	10.414%	$223.9086	$223.91	$223.90	$223.90
Purchase #3	$111.76	10.775%	$123.8021	$123.80	$123.80	$123.80
Purchase #4	$144.82	9.700%	$158.8675	$158.87	$158.85	$158.90
Purchase #5	$178.92	7.335%	$192.0438	$192.04	$192.05	$192.00
Purchase #6	$13.28	4.764%	$13.9127	$13.91	$13.90	$13.90
Purchase #7	$38.50	8.302%	$41.6963	$41.70	$41.70	$41.70
7 purchase totals =	$710.71		$775.9511	$775.95	$775.90	$775.90