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	$120.76	4.664%	$126.3922	$126.39	$126.40	$126.40
Purchase #2	$215.78	11.866%	$241.3845	$241.38	$241.40	$241.40
Purchase #3	$91.90	9.800%	$100.9062	$100.91	$100.90	$100.90
Purchase #4	$250.52	5.855%	$265.1879	$265.19	$265.20	$265.20
Purchase #5	$65.91	11.394%	$73.4198	$73.42	$73.40	$73.40
Purchase #6	$102.82	13.382%	$116.5794	$116.58	$116.60	$116.60
Purchase #7	$168.41	3.429%	$174.1848	$174.18	$174.20	$174.20
7 purchase totals =	$1,016.10		$1,098.0548	$1,098.05	$1,098.10	$1,098.10