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	$244.88	6.559%	$260.9417	$260.94	$260.95	$260.90
Purchase #2	$90.51	13.856%	$103.0511	$103.05	$103.05	$103.10
Purchase #3	$154.52	9.341%	$168.9537	$168.95	$168.95	$169.00
Purchase #4	$178.40	8.723%	$193.9618	$193.96	$193.95	$194.00
Purchase #5	$100.90	7.725%	$108.6945	$108.69	$108.70	$108.70
Purchase #6	$116.51	12.497%	$131.0703	$131.07	$131.05	$131.10
Purchase #7	$92.43	12.105%	$103.6187	$103.62	$103.60	$103.60
7 purchase totals =	$978.15		$1,070.2918	$1,070.28	$1,070.25	$1,070.40