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	$69.42	4.534%	$72.5675	$72.57	$72.55	$72.60
Purchase #2	$29.26	4.786%	$30.6604	$30.66	$30.65	$30.70
Purchase #3	$133.42	6.447%	$142.0216	$142.02	$142.00	$142.00
Purchase #4	$108.94	13.122%	$123.2351	$123.24	$123.25	$123.20
Purchase #5	$123.90	10.574%	$137.0012	$137.00	$137.00	$137.00
Purchase #6	$133.42	4.532%	$139.4666	$139.47	$139.45	$139.50
Purchase #7	$191.48	7.379%	$205.6093	$205.61	$205.60	$205.60
7 purchase totals =	$789.84		$850.5617	$850.57	$850.50	$850.60