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	$122.60	13.842%	$139.5703	$139.57	$139.55	$139.60
Purchase #2	$160.95	13.111%	$182.0522	$182.05	$182.05	$182.10
Purchase #3	$65.88	9.683%	$72.2592	$72.26	$72.25	$72.30
Purchase #4	$94.71	5.794%	$100.1975	$100.20	$100.20	$100.20
Purchase #5	$148.71	6.630%	$158.5695	$158.57	$158.55	$158.60
Purchase #6	$109.33	11.311%	$121.6963	$121.70	$121.70	$121.70
Purchase #7	$42.48	9.686%	$46.5946	$46.59	$46.60	$46.60
7 purchase totals =	$744.66		$820.9396	$820.94	$820.90	$821.10