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	$144.89	6.825%	$154.7787	$154.78	$154.80	$154.80
Purchase #2	$49.34	11.344%	$54.9371	$54.94	$54.95	$54.90
Purchase #3	$158.61	12.262%	$178.0588	$178.06	$178.05	$178.10
Purchase #4	$222.80	6.832%	$238.0217	$238.02	$238.00	$238.00
Purchase #5	$84.80	11.477%	$94.5325	$94.53	$94.55	$94.50
Purchase #6	$99.93	5.228%	$105.1543	$105.15	$105.15	$105.20
Purchase #7	$143.95	10.120%	$158.5177	$158.52	$158.50	$158.50
7 purchase totals =	$904.32		$984.0008	$984.00	$984.00	$984.00