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	$116.36	3.379%	$120.2918	$120.29	$120.30	$120.30
Purchase #2	$85.45	4.779%	$89.5337	$89.53	$89.55	$89.50
Purchase #3	$81.63	7.682%	$87.9008	$87.90	$87.90	$87.90
Purchase #4	$13.26	3.445%	$13.7168	$13.72	$13.70	$13.70
Purchase #5	$134.96	3.149%	$139.2099	$139.21	$139.20	$139.20
Purchase #6	$21.76	9.637%	$23.857	$23.86	$23.85	$23.90
Purchase #7	$99.36	10.236%	$109.5305	$109.53	$109.55	$109.50
7 purchase totals =	$552.78		$584.0405	$584.04	$584.05	$584.00