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	$27.69	12.343%	$31.1078	$31.11	$31.10	$31.10
Purchase #2	$151.59	13.416%	$171.9273	$171.93	$171.95	$171.90
Purchase #3	$247.86	3.514%	$256.5698	$256.57	$256.55	$256.60
Purchase #4	$103.81	10.196%	$114.3945	$114.39	$114.40	$114.40
Purchase #5	$43.86	9.731%	$48.128	$48.13	$48.15	$48.10
Purchase #6	$10.55	8.219%	$11.4171	$11.42	$11.40	$11.40
Purchase #7	$87.45	8.690%	$95.0494	$95.05	$95.05	$95.00
7 purchase totals =	$672.81		$728.5939	$728.60	$728.60	$728.50