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	$38.79	12.220%	$43.5301	$43.53	$43.55	$43.50
Purchase #2	$130.48	10.265%	$143.8738	$143.87	$143.85	$143.90
Purchase #3	$199.49	6.563%	$212.5825	$212.58	$212.60	$212.60
Purchase #4	$121.81	10.753%	$134.9082	$134.91	$134.90	$134.90
Purchase #5	$169.45	13.804%	$192.8409	$192.84	$192.85	$192.80
Purchase #6	$97.31	3.632%	$100.8443	$100.84	$100.85	$100.80
Purchase #7	$232.90	10.330%	$256.9586	$256.96	$256.95	$257.00
7 purchase totals =	$990.23		$1,085.5384	$1,085.53	$1,085.55	$1,085.50