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	$10.39	13.207%	$11.7622	$11.76	$11.75	$11.80
Purchase #2	$37.73	13.576%	$42.8522	$42.85	$42.85	$42.90
Purchase #3	$219.49	8.790%	$238.7832	$238.78	$238.80	$238.80
Purchase #4	$139.43	3.820%	$144.7562	$144.76	$144.75	$144.80
Purchase #5	$63.85	9.346%	$69.8174	$69.82	$69.80	$69.80
Purchase #6	$156.42	7.712%	$168.4831	$168.48	$168.50	$168.50
Purchase #7	$148.26	4.547%	$155.0014	$155.00	$155.00	$155.00
7 purchase totals =	$775.57		$831.4557	$831.45	$831.45	$831.60