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	$19.46	10.243%	$21.4533	$21.45	$21.45	$21.50
Purchase #2	$67.43	9.753%	$74.0064	$74.01	$74.00	$74.00
Purchase #3	$231.57	9.351%	$253.2241	$253.22	$253.20	$253.20
Purchase #4	$222.52	7.153%	$238.4369	$238.44	$238.45	$238.40
Purchase #5	$38.97	9.332%	$42.6067	$42.61	$42.60	$42.60
Purchase #6	$106.53	5.389%	$112.2709	$112.27	$112.25	$112.30
Purchase #7	$57.83	9.781%	$63.4864	$63.49	$63.50	$63.50
7 purchase totals =	$744.31		$805.4847	$805.49	$805.45	$805.50