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	$106.43	6.421%	$113.2639	$113.26	$113.25	$113.30
Purchase #2	$215.62	8.758%	$234.504	$234.50	$234.50	$234.50
Purchase #3	$166.76	3.859%	$173.1953	$173.20	$173.20	$173.20
Purchase #4	$75.75	10.293%	$83.5469	$83.55	$83.55	$83.50
Purchase #5	$13.52	13.678%	$15.3693	$15.37	$15.35	$15.40
Purchase #6	$52.58	13.363%	$59.6063	$59.61	$59.60	$59.60
Purchase #7	$87.96	13.617%	$99.9375	$99.94	$99.95	$99.90
7 purchase totals =	$718.62		$779.4232	$779.43	$779.40	$779.40