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	$238.45	8.205%	$258.0148	$258.01	$258.00	$258.00
Purchase #2	$105.85	5.306%	$111.4664	$111.47	$111.45	$111.50
Purchase #3	$126.46	13.792%	$143.9014	$143.90	$143.90	$143.90
Purchase #4	$17.89	5.217%	$18.8233	$18.82	$18.80	$18.80
Purchase #5	$237.58	9.364%	$259.827	$259.83	$259.85	$259.80
Purchase #6	$63.89	9.396%	$69.8931	$69.89	$69.90	$69.90
Purchase #7	$120.62	13.190%	$136.5298	$136.53	$136.55	$136.50
7 purchase totals =	$910.74		$998.4558	$998.45	$998.45	$998.40