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	$11.46	13.471%	$13.0038	$13.00	$13.00	$13.00
Purchase #2	$239.45	9.645%	$262.545	$262.55	$262.55	$262.50
Purchase #3	$95.27	10.127%	$104.918	$104.92	$104.90	$104.90
Purchase #4	$164.70	10.807%	$182.4991	$182.50	$182.50	$182.50
Purchase #5	$75.43	7.609%	$81.1695	$81.17	$81.15	$81.20
Purchase #6	$35.63	6.224%	$37.8476	$37.85	$37.85	$37.80
Purchase #7	$189.39	5.866%	$200.4996	$200.50	$200.50	$200.50
7 purchase totals =	$811.33		$882.4826	$882.49	$882.45	$882.40