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	$38.55	13.689%	$43.8271	$43.83	$43.85	$43.80
Purchase #2	$94.68	10.846%	$104.949	$104.95	$104.95	$104.90
Purchase #3	$100.87	4.784%	$105.6956	$105.70	$105.70	$105.70
Purchase #4	$69.79	10.305%	$76.9819	$76.98	$77.00	$77.00
Purchase #5	$51.26	8.240%	$55.4838	$55.48	$55.50	$55.50
Purchase #6	$184.97	3.691%	$191.7972	$191.80	$191.80	$191.80
Purchase #7	$18.47	12.139%	$20.7121	$20.71	$20.70	$20.70
7 purchase totals =	$558.59		$599.4467	$599.45	$599.50	$599.40