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	$165.86	10.338%	$183.0066	$183.01	$183.00	$183.00
Purchase #2	$247.75	13.286%	$280.6661	$280.67	$280.65	$280.70
Purchase #3	$127.77	13.509%	$145.0304	$145.03	$145.05	$145.00
Purchase #4	$24.84	10.693%	$27.4961	$27.50	$27.50	$27.50
Purchase #5	$206.53	7.437%	$221.8896	$221.89	$221.90	$221.90
Purchase #6	$83.47	5.300%	$87.8939	$87.89	$87.90	$87.90
Purchase #7	$120.66	8.217%	$130.5746	$130.57	$130.55	$130.60
7 purchase totals =	$976.88		$1,076.5573	$1,076.56	$1,076.55	$1,076.60