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	$230.48	12.130%	$258.4372	$258.44	$258.45	$258.40
Purchase #2	$63.83	12.190%	$71.6109	$71.61	$71.60	$71.60
Purchase #3	$151.76	11.759%	$169.6055	$169.61	$169.60	$169.60
Purchase #4	$63.94	4.570%	$66.8621	$66.86	$66.85	$66.90
Purchase #5	$128.54	10.143%	$141.5778	$141.58	$141.60	$141.60
Purchase #6	$18.43	12.759%	$20.7815	$20.78	$20.80	$20.80
Purchase #7	$134.64	5.255%	$141.7153	$141.72	$141.70	$141.70
7 purchase totals =	$791.62		$870.5903	$870.60	$870.60	$870.60