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	$113.62	8.744%	$123.5549	$123.55	$123.55	$123.60
Purchase #2	$108.75	13.172%	$123.0746	$123.07	$123.05	$123.10
Purchase #3	$131.67	12.262%	$147.8154	$147.82	$147.80	$147.80
Purchase #4	$103.46	12.222%	$116.1049	$116.10	$116.10	$116.10
Purchase #5	$232.83	12.593%	$262.1503	$262.15	$262.15	$262.20
Purchase #6	$150.47	5.319%	$158.4735	$158.47	$158.45	$158.50
Purchase #7	$35.68	9.863%	$39.1991	$39.20	$39.20	$39.20
7 purchase totals =	$876.48		$970.3727	$970.36	$970.30	$970.50