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	$245.70	8.161%	$265.7516	$265.75	$265.75	$265.80
Purchase #2	$15.40	13.495%	$17.4782	$17.48	$17.50	$17.50
Purchase #3	$82.78	8.675%	$89.9612	$89.96	$89.95	$90.00
Purchase #4	$148.83	4.186%	$155.06	$155.06	$155.05	$155.10
Purchase #5	$12.87	5.647%	$13.5968	$13.60	$13.60	$13.60
Purchase #6	$56.76	3.214%	$58.5843	$58.58	$58.60	$58.60
Purchase #7	$37.40	5.529%	$39.4678	$39.47	$39.45	$39.50
7 purchase totals =	$599.74		$639.8999	$639.90	$639.90	$640.10