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	$131.27	11.230%	$146.0116	$146.01	$146.00	$146.00
Purchase #2	$73.75	6.154%	$78.2886	$78.29	$78.30	$78.30
Purchase #3	$126.47	5.504%	$133.4309	$133.43	$133.45	$133.40
Purchase #4	$19.78	13.747%	$22.4992	$22.50	$22.50	$22.50
Purchase #5	$148.76	6.759%	$158.8147	$158.81	$158.80	$158.80
Purchase #6	$102.87	8.519%	$111.6335	$111.63	$111.65	$111.60
Purchase #7	$5.94	11.176%	$6.6039	$6.60	$6.60	$6.60
7 purchase totals =	$608.84		$657.2824	$657.27	$657.30	$657.20