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	$14.51	9.105%	$15.8311	$15.83	$15.85	$15.80
Purchase #2	$219.64	10.136%	$241.9027	$241.90	$241.90	$241.90
Purchase #3	$222.92	8.385%	$241.6118	$241.61	$241.60	$241.60
Purchase #4	$194.79	13.856%	$221.7801	$221.78	$221.80	$221.80
Purchase #5	$122.98	3.124%	$126.8219	$126.82	$126.80	$126.80
Purchase #6	$46.54	9.579%	$50.9981	$51.00	$51.00	$51.00
Purchase #7	$80.78	11.355%	$89.9526	$89.95	$89.95	$90.00
7 purchase totals =	$902.16		$988.8983	$988.89	$988.90	$988.90