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	$83.52	7.576%	$89.8475	$89.85	$89.85	$89.80
Purchase #2	$229.98	3.679%	$238.441	$238.44	$238.45	$238.40
Purchase #3	$7.33	7.126%	$7.8523	$7.85	$7.85	$7.90
Purchase #4	$91.89	13.526%	$104.319	$104.32	$104.30	$104.30
Purchase #5	$115.27	5.145%	$121.2006	$121.20	$121.20	$121.20
Purchase #6	$14.90	4.574%	$15.5815	$15.58	$15.60	$15.60
Purchase #7	$35.53	11.311%	$39.5488	$39.55	$39.55	$39.50
7 purchase totals =	$578.42		$616.7907	$616.79	$616.80	$616.70