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	$27.79	11.264%	$30.9203	$30.92	$30.90	$30.90
Purchase #2	$126.79	12.127%	$142.1658	$142.17	$142.15	$142.20
Purchase #3	$195.53	11.622%	$218.2545	$218.25	$218.25	$218.30
Purchase #4	$48.25	13.225%	$54.6311	$54.63	$54.65	$54.60
Purchase #5	$106.98	11.477%	$119.2581	$119.26	$119.25	$119.30
Purchase #6	$200.25	11.240%	$222.7581	$222.76	$222.75	$222.80
Purchase #7	$179.76	8.176%	$194.4572	$194.46	$194.45	$194.50
7 purchase totals =	$885.35		$982.4451	$982.45	$982.40	$982.60