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	$15.46	13.798%	$17.5932	$17.59	$17.60	$17.60
Purchase #2	$176.58	4.610%	$184.7203	$184.72	$184.70	$184.70
Purchase #3	$203.39	11.832%	$227.4551	$227.46	$227.45	$227.50
Purchase #4	$104.92	7.260%	$112.5372	$112.54	$112.55	$112.50
Purchase #5	$118.94	3.799%	$123.4585	$123.46	$123.45	$123.50
Purchase #6	$207.76	7.143%	$222.6003	$222.60	$222.60	$222.60
Purchase #7	$206.38	6.357%	$219.4996	$219.50	$219.50	$219.50
7 purchase totals =	$1,033.43		$1,107.8642	$1,107.87	$1,107.85	$1,107.90