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	$166.93	3.194%	$172.2617	$172.26	$172.25	$172.30
Purchase #2	$14.75	4.777%	$15.4546	$15.45	$15.45	$15.50
Purchase #3	$57.43	6.378%	$61.0929	$61.09	$61.10	$61.10
Purchase #4	$138.51	10.176%	$152.6048	$152.60	$152.60	$152.60
Purchase #5	$244.91	13.802%	$278.7125	$278.71	$278.70	$278.70
Purchase #6	$224.70	13.679%	$255.4367	$255.44	$255.45	$255.40
Purchase #7	$37.76	8.181%	$40.8491	$40.85	$40.85	$40.80
7 purchase totals =	$884.99		$976.4123	$976.40	$976.40	$976.40