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	$122.85	13.547%	$139.4925	$139.49	$139.50	$139.50
Purchase #2	$163.28	3.314%	$168.6911	$168.69	$168.70	$168.70
Purchase #3	$37.90	12.371%	$42.5886	$42.59	$42.60	$42.60
Purchase #4	$63.81	4.189%	$66.483	$66.48	$66.50	$66.50
Purchase #5	$145.79	11.376%	$162.3751	$162.38	$162.40	$162.40
Purchase #6	$120.50	6.430%	$128.2482	$128.25	$128.25	$128.20
Purchase #7	$144.89	11.778%	$161.9551	$161.96	$161.95	$162.00
7 purchase totals =	$799.02		$869.8336	$869.84	$869.90	$869.90