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	$37.52	6.667%	$40.0215	$40.02	$40.00	$40.00
Purchase #2	$131.88	7.405%	$141.6457	$141.65	$141.65	$141.60
Purchase #3	$98.48	12.845%	$111.1298	$111.13	$111.15	$111.10
Purchase #4	$213.44	13.699%	$242.6791	$242.68	$242.70	$242.70
Purchase #5	$45.80	10.353%	$50.5417	$50.54	$50.55	$50.50
Purchase #6	$95.41	10.867%	$105.7782	$105.78	$105.80	$105.80
Purchase #7	$46.89	8.547%	$50.8977	$50.90	$50.90	$50.90
7 purchase totals =	$669.42		$742.6937	$742.70	$742.75	$742.60