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	$118.57	8.646%	$128.8216	$128.82	$128.80	$128.80
Purchase #2	$15.86	8.516%	$17.2106	$17.21	$17.20	$17.20
Purchase #3	$66.55	9.396%	$72.803	$72.80	$72.80	$72.80
Purchase #4	$153.96	7.353%	$165.2807	$165.28	$165.30	$165.30
Purchase #5	$137.96	10.357%	$152.2485	$152.25	$152.25	$152.20
Purchase #6	$104.35	10.108%	$114.8977	$114.90	$114.90	$114.90
Purchase #7	$224.87	13.672%	$255.6142	$255.61	$255.60	$255.60
7 purchase totals =	$822.12		$906.8763	$906.87	$906.85	$906.80