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	$9.77	7.508%	$10.5035	$10.50	$10.50	$10.50
Purchase #2	$9.80	13.770%	$11.1495	$11.15	$11.15	$11.10
Purchase #3	$202.83	9.519%	$222.1374	$222.14	$222.15	$222.10
Purchase #4	$122.47	10.490%	$135.3171	$135.32	$135.30	$135.30
Purchase #5	$84.41	6.176%	$89.6232	$89.62	$89.60	$89.60
Purchase #6	$166.90	13.365%	$189.2062	$189.21	$189.20	$189.20
Purchase #7	$43.72	6.328%	$46.4866	$46.49	$46.50	$46.50
7 purchase totals =	$639.90		$704.4235	$704.43	$704.40	$704.30