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	$83.61	6.871%	$89.3548	$89.35	$89.35	$89.40
Purchase #2	$171.45	11.838%	$191.7463	$191.75	$191.75	$191.70
Purchase #3	$44.82	4.567%	$46.8669	$46.87	$46.85	$46.90
Purchase #4	$102.34	8.766%	$111.3111	$111.31	$111.30	$111.30
Purchase #5	$86.35	9.412%	$94.4773	$94.48	$94.50	$94.50
Purchase #6	$227.29	13.276%	$257.465	$257.47	$257.45	$257.50
Purchase #7	$157.49	4.587%	$164.7141	$164.71	$164.70	$164.70
7 purchase totals =	$873.35		$955.9355	$955.94	$955.90	$956.00