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	$239.48	13.105%	$270.8639	$270.86	$270.85	$270.90
Purchase #2	$95.58	8.301%	$103.5141	$103.51	$103.50	$103.50
Purchase #3	$77.32	11.190%	$85.9721	$85.97	$85.95	$86.00
Purchase #4	$100.26	13.509%	$113.8041	$113.80	$113.80	$113.80
Purchase #5	$59.86	10.360%	$66.0615	$66.06	$66.05	$66.10
Purchase #6	$76.37	12.491%	$85.9094	$85.91	$85.90	$85.90
Purchase #7	$145.96	7.200%	$156.4691	$156.47	$156.45	$156.50
7 purchase totals =	$794.83		$882.5942	$882.58	$882.50	$882.70