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	$231.37	10.341%	$255.296	$255.30	$255.30	$255.30
Purchase #2	$33.33	4.725%	$34.9048	$34.90	$34.90	$34.90
Purchase #3	$241.38	6.239%	$256.4397	$256.44	$256.45	$256.40
Purchase #4	$155.57	10.814%	$172.3933	$172.39	$172.40	$172.40
Purchase #5	$175.91	7.138%	$188.4665	$188.47	$188.45	$188.50
Purchase #6	$44.67	4.327%	$46.6029	$46.60	$46.60	$46.60
Purchase #7	$125.32	9.483%	$137.2041	$137.20	$137.20	$137.20
7 purchase totals =	$1,007.55		$1,091.3073	$1,091.30	$1,091.30	$1,091.30