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	$112.96	5.756%	$119.462	$119.46	$119.45	$119.50
Purchase #2	$34.30	10.571%	$37.9259	$37.93	$37.95	$37.90
Purchase #3	$113.51	11.545%	$126.6147	$126.61	$126.60	$126.60
Purchase #4	$157.39	4.137%	$163.9012	$163.90	$163.90	$163.90
Purchase #5	$37.91	6.840%	$40.503	$40.50	$40.50	$40.50
Purchase #6	$111.83	7.242%	$119.9287	$119.93	$119.95	$119.90
Purchase #7	$54.52	6.688%	$58.1663	$58.17	$58.15	$58.20
7 purchase totals =	$622.42		$666.5018	$666.50	$666.50	$666.50