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	$123.32	12.481%	$138.7116	$138.71	$138.70	$138.70
Purchase #2	$112.38	9.779%	$123.3696	$123.37	$123.35	$123.40
Purchase #3	$16.88	3.779%	$17.5179	$17.52	$17.50	$17.50
Purchase #4	$205.30	8.540%	$222.8326	$222.83	$222.85	$222.80
Purchase #5	$140.45	7.521%	$151.0132	$151.01	$151.00	$151.00
Purchase #6	$140.49	7.582%	$151.142	$151.14	$151.15	$151.10
Purchase #7	$215.94	4.391%	$225.4219	$225.42	$225.40	$225.40
7 purchase totals =	$954.76		$1,030.0088	$1,030.00	$1,029.95	$1,029.90