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	$122.48	11.221%	$136.2235	$136.22	$136.20	$136.20
Purchase #2	$131.90	12.600%	$148.5194	$148.52	$148.50	$148.50
Purchase #3	$49.81	8.429%	$54.0085	$54.01	$54.00	$54.00
Purchase #4	$14.75	4.671%	$15.439	$15.44	$15.45	$15.40
Purchase #5	$249.71	10.367%	$275.5974	$275.60	$275.60	$275.60
Purchase #6	$175.56	10.839%	$194.5889	$194.59	$194.60	$194.60
Purchase #7	$128.79	10.146%	$141.857	$141.86	$141.85	$141.90
7 purchase totals =	$873.00		$966.2337	$966.24	$966.20	$966.20