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	$38.75	4.242%	$40.3938	$40.39	$40.40	$40.40
Purchase #2	$94.67	12.440%	$106.4469	$106.45	$106.45	$106.40
Purchase #3	$133.81	8.698%	$145.4488	$145.45	$145.45	$145.40
Purchase #4	$90.66	4.335%	$94.5901	$94.59	$94.60	$94.60
Purchase #5	$33.76	5.440%	$35.5965	$35.60	$35.60	$35.60
Purchase #6	$32.63	4.391%	$34.0628	$34.06	$34.05	$34.10
Purchase #7	$104.81	6.429%	$111.5482	$111.55	$111.55	$111.50
7 purchase totals =	$529.09		$568.0871	$568.09	$568.10	$568.00