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	$34.32	11.766%	$38.3581	$38.36	$38.35	$38.40
Purchase #2	$123.30	13.535%	$139.9887	$139.99	$140.00	$140.00
Purchase #3	$78.61	6.246%	$83.52	$83.52	$83.50	$83.50
Purchase #4	$67.27	3.832%	$69.8478	$69.85	$69.85	$69.80
Purchase #5	$72.44	8.393%	$78.5199	$78.52	$78.50	$78.50
Purchase #6	$172.29	12.336%	$193.5437	$193.54	$193.55	$193.50
Purchase #7	$10.30	9.465%	$11.2749	$11.27	$11.25	$11.30
7 purchase totals =	$558.53		$615.0531	$615.05	$615.00	$615.00