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	$44.55	6.689%	$47.5299	$47.53	$47.55	$47.50
Purchase #2	$246.71	4.189%	$257.0447	$257.04	$257.05	$257.00
Purchase #3	$38.38	8.143%	$41.5053	$41.51	$41.50	$41.50
Purchase #4	$209.75	7.868%	$226.2531	$226.25	$226.25	$226.30
Purchase #5	$34.55	5.550%	$36.4675	$36.47	$36.45	$36.50
Purchase #6	$75.56	4.421%	$78.9005	$78.90	$78.90	$78.90
Purchase #7	$71.90	9.493%	$78.7255	$78.73	$78.75	$78.70
7 purchase totals =	$721.40		$766.4265	$766.43	$766.45	$766.40