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	$62.49	12.386%	$70.23	$70.23	$70.25	$70.20
Purchase #2	$137.77	11.493%	$153.6039	$153.60	$153.60	$153.60
Purchase #3	$29.85	3.272%	$30.8267	$30.83	$30.85	$30.80
Purchase #4	$68.60	3.515%	$71.0113	$71.01	$71.00	$71.00
Purchase #5	$52.28	13.418%	$59.2949	$59.29	$59.30	$59.30
Purchase #6	$25.68	13.178%	$29.0641	$29.06	$29.05	$29.10
Purchase #7	$222.25	13.832%	$252.9916	$252.99	$253.00	$253.00
7 purchase totals =	$598.92		$667.0225	$667.01	$667.05	$667.00