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	$37.70	13.758%	$42.8868	$42.89	$42.90	$42.90
Purchase #2	$167.89	10.716%	$185.8811	$185.88	$185.90	$185.90
Purchase #3	$77.67	3.174%	$80.1352	$80.14	$80.15	$80.10
Purchase #4	$211.48	7.509%	$227.36	$227.36	$227.35	$227.40
Purchase #5	$83.65	12.196%	$93.852	$93.85	$93.85	$93.90
Purchase #6	$58.52	7.717%	$63.036	$63.04	$63.05	$63.00
Purchase #7	$80.31	3.123%	$82.8181	$82.82	$82.80	$82.80
7 purchase totals =	$717.22		$775.9692	$775.98	$776.00	$776.00