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	$18.35	6.558%	$19.5534	$19.55	$19.55	$19.60
Purchase #2	$53.28	5.466%	$56.1923	$56.19	$56.20	$56.20
Purchase #3	$71.37	11.369%	$79.4841	$79.48	$79.50	$79.50
Purchase #4	$210.94	7.848%	$227.4946	$227.49	$227.50	$227.50
Purchase #5	$14.66	6.374%	$15.5944	$15.59	$15.60	$15.60
Purchase #6	$80.66	10.455%	$89.093	$89.09	$89.10	$89.10
Purchase #7	$10.54	10.122%	$11.6069	$11.61	$11.60	$11.60
7 purchase totals =	$459.80		$499.0187	$499.00	$499.05	$499.10