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	$37.78	12.806%	$42.6181	$42.62	$42.60	$42.60
Purchase #2	$82.45	5.387%	$86.8916	$86.89	$86.90	$86.90
Purchase #3	$60.55	5.762%	$64.0389	$64.04	$64.05	$64.00
Purchase #4	$90.84	9.749%	$99.696	$99.70	$99.70	$99.70
Purchase #5	$205.70	5.766%	$217.5607	$217.56	$217.55	$217.60
Purchase #6	$9.90	6.559%	$10.5493	$10.55	$10.55	$10.50
Purchase #7	$30.53	7.294%	$32.7569	$32.76	$32.75	$32.80
7 purchase totals =	$517.75		$554.1115	$554.12	$554.10	$554.10