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	$35.87	12.772%	$40.4513	$40.45	$40.45	$40.50
Purchase #2	$106.89	13.777%	$121.6162	$121.62	$121.60	$121.60
Purchase #3	$30.93	13.339%	$35.0558	$35.06	$35.05	$35.10
Purchase #4	$70.27	4.831%	$73.6647	$73.66	$73.65	$73.70
Purchase #5	$186.78	5.326%	$196.7279	$196.73	$196.75	$196.70
Purchase #6	$10.55	8.266%	$11.4221	$11.42	$11.40	$11.40
Purchase #7	$78.50	6.275%	$83.4259	$83.43	$83.45	$83.40
7 purchase totals =	$519.79		$562.3639	$562.37	$562.35	$562.40