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	$85.92	4.599%	$89.8715	$89.87	$89.85	$89.90
Purchase #2	$76.78	7.828%	$82.7903	$82.79	$82.80	$82.80
Purchase #3	$87.79	11.661%	$98.0272	$98.03	$98.05	$98.00
Purchase #4	$237.48	4.233%	$247.5325	$247.53	$247.55	$247.50
Purchase #5	$119.32	11.329%	$132.8378	$132.84	$132.85	$132.80
Purchase #6	$103.60	8.624%	$112.5345	$112.53	$112.55	$112.50
Purchase #7	$68.46	11.757%	$76.5088	$76.51	$76.50	$76.50
7 purchase totals =	$779.35		$840.1026	$840.10	$840.15	$840.00