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	$133.59	12.670%	$150.5159	$150.52	$150.50	$150.50
Purchase #2	$75.69	11.178%	$84.1506	$84.15	$84.15	$84.20
Purchase #3	$116.83	8.680%	$126.9708	$126.97	$126.95	$127.00
Purchase #4	$28.47	8.595%	$30.917	$30.92	$30.90	$30.90
Purchase #5	$89.45	6.743%	$95.4816	$95.48	$95.50	$95.50
Purchase #6	$247.85	13.219%	$280.6133	$280.61	$280.60	$280.60
Purchase #7	$91.92	8.288%	$99.5383	$99.54	$99.55	$99.50
7 purchase totals =	$783.80		$868.1875	$868.19	$868.15	$868.20