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	$18.60	11.644%	$20.7658	$20.77	$20.75	$20.80
Purchase #2	$38.77	9.638%	$42.5067	$42.51	$42.50	$42.50
Purchase #3	$196.74	9.678%	$215.7805	$215.78	$215.80	$215.80
Purchase #4	$11.93	4.179%	$12.4286	$12.43	$12.45	$12.40
Purchase #5	$87.77	9.458%	$96.0713	$96.07	$96.05	$96.10
Purchase #6	$6.95	8.311%	$7.5276	$7.53	$7.55	$7.50
Purchase #7	$150.90	12.574%	$169.8742	$169.87	$169.85	$169.90
7 purchase totals =	$511.66		$564.9547	$564.96	$564.95	$565.00