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	$139.56	7.806%	$150.4541	$150.45	$150.45	$150.50
Purchase #2	$52.83	11.467%	$58.888	$58.89	$58.90	$58.90
Purchase #3	$134.84	7.581%	$145.0622	$145.06	$145.05	$145.10
Purchase #4	$88.78	13.810%	$101.0405	$101.04	$101.05	$101.00
Purchase #5	$172.47	6.679%	$183.9893	$183.99	$184.00	$184.00
Purchase #6	$29.94	8.520%	$32.4909	$32.49	$32.50	$32.50
Purchase #7	$101.68	9.422%	$111.2603	$111.26	$111.25	$111.30
7 purchase totals =	$720.10		$783.1853	$783.18	$783.20	$783.30