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	$12.87	3.280%	$13.2921	$13.29	$13.30	$13.30
Purchase #2	$209.79	12.568%	$236.1564	$236.16	$236.15	$236.20
Purchase #3	$44.94	4.283%	$46.8648	$46.86	$46.85	$46.90
Purchase #4	$42.70	13.506%	$48.4671	$48.47	$48.45	$48.50
Purchase #5	$87.28	3.215%	$90.0861	$90.09	$90.10	$90.10
Purchase #6	$220.70	11.278%	$245.5905	$245.59	$245.60	$245.60
Purchase #7	$28.78	10.874%	$31.9095	$31.91	$31.90	$31.90
7 purchase totals =	$647.06		$712.3665	$712.37	$712.35	$712.50