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	$34.90	11.797%	$39.0172	$39.02	$39.00	$39.00
Purchase #2	$148.27	7.145%	$158.8639	$158.86	$158.85	$158.90
Purchase #3	$131.79	4.310%	$137.4701	$137.47	$137.45	$137.50
Purchase #4	$16.52	8.558%	$17.9338	$17.93	$17.95	$17.90
Purchase #5	$235.55	6.748%	$251.4449	$251.44	$251.45	$251.40
Purchase #6	$6.56	4.499%	$6.8551	$6.86	$6.85	$6.90
Purchase #7	$85.31	4.772%	$89.381	$89.38	$89.40	$89.40
7 purchase totals =	$658.90		$700.9660	$700.96	$700.95	$701.00