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	$77.42	6.474%	$82.4322	$82.43	$82.45	$82.40
Purchase #2	$216.78	10.679%	$239.9299	$239.93	$239.95	$239.90
Purchase #3	$47.45	7.619%	$51.0652	$51.07	$51.05	$51.10
Purchase #4	$182.59	3.863%	$189.6435	$189.64	$189.65	$189.60
Purchase #5	$158.93	5.828%	$168.1924	$168.19	$168.20	$168.20
Purchase #6	$79.81	13.233%	$90.3713	$90.37	$90.35	$90.40
Purchase #7	$57.77	9.745%	$63.3997	$63.40	$63.40	$63.40
7 purchase totals =	$820.75		$885.0342	$885.03	$885.05	$885.00