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	10.630%	$183.4909	$183.49	$183.50	$183.50
Purchase #2	$56.31	5.859%	$59.6092	$59.61	$59.60	$59.60
Purchase #3	$137.62	5.347%	$144.9785	$144.98	$145.00	$145.00
Purchase #4	$221.29	7.267%	$237.3711	$237.37	$237.35	$237.40
Purchase #5	$112.50	6.325%	$119.6156	$119.62	$119.60	$119.60
Purchase #6	$43.35	11.556%	$48.3595	$48.36	$48.35	$48.40
Purchase #7	$235.33	4.734%	$246.4705	$246.47	$246.45	$246.50
7 purchase totals =	$972.26		$1,039.8953	$1,039.90	$1,039.85	$1,040.00