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	$236.91	10.724%	$262.3162	$262.32	$262.30	$262.30
Purchase #2	$54.37	8.627%	$59.0605	$59.06	$59.05	$59.10
Purchase #3	$111.78	13.180%	$126.5126	$126.51	$126.50	$126.50
Purchase #4	$18.40	11.642%	$20.5421	$20.54	$20.55	$20.50
Purchase #5	$6.99	8.393%	$7.5767	$7.58	$7.60	$7.60
Purchase #6	$13.87	8.212%	$15.009	$15.01	$15.00	$15.00
Purchase #7	$81.69	9.476%	$89.4309	$89.43	$89.45	$89.40
7 purchase totals =	$524.01		$580.4480	$580.45	$580.45	$580.40