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	$75.40	12.757%	$85.0188	$85.02	$85.00	$85.00
Purchase #2	$18.86	6.631%	$20.1106	$20.11	$20.10	$20.10
Purchase #3	$91.99	8.856%	$100.1366	$100.14	$100.15	$100.10
Purchase #4	$9.86	11.151%	$10.9595	$10.96	$10.95	$11.00
Purchase #5	$121.25	7.575%	$130.4347	$130.43	$130.45	$130.40
Purchase #6	$217.82	10.462%	$240.6083	$240.61	$240.60	$240.60
Purchase #7	$130.48	7.769%	$140.617	$140.62	$140.60	$140.60
7 purchase totals =	$665.66		$727.8855	$727.89	$727.85	$727.80