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	$12.42	7.460%	$13.3465	$13.35	$13.35	$13.30
Purchase #2	$86.86	9.304%	$94.9415	$94.94	$94.95	$94.90
Purchase #3	$153.39	12.335%	$172.3107	$172.31	$172.30	$172.30
Purchase #4	$210.50	7.491%	$226.2686	$226.27	$226.25	$226.30
Purchase #5	$93.54	11.518%	$104.3139	$104.31	$104.30	$104.30
Purchase #6	$205.52	8.159%	$222.2884	$222.29	$222.30	$222.30
Purchase #7	$134.81	12.356%	$151.4671	$151.47	$151.45	$151.50
7 purchase totals =	$897.04		$984.9367	$984.94	$984.90	$984.90