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	$31.30	9.614%	$34.3092	$34.31	$34.30	$34.30
Purchase #2	$158.48	6.393%	$168.6116	$168.61	$168.60	$168.60
Purchase #3	$228.72	13.146%	$258.7875	$258.79	$258.80	$258.80
Purchase #4	$48.83	9.669%	$53.5514	$53.55	$53.55	$53.60
Purchase #5	$137.50	4.748%	$144.0285	$144.03	$144.05	$144.00
Purchase #6	$247.37	3.329%	$255.6049	$255.60	$255.60	$255.60
Purchase #7	$192.51	10.479%	$212.6831	$212.68	$212.70	$212.70
7 purchase totals =	$1,044.71		$1,127.5762	$1,127.57	$1,127.60	$1,127.60