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	$35.42	13.116%	$40.0657	$40.07	$40.05	$40.10
Purchase #2	$103.83	10.275%	$114.4985	$114.50	$114.50	$114.50
Purchase #3	$76.40	5.317%	$80.4622	$80.46	$80.45	$80.50
Purchase #4	$117.77	8.189%	$127.4142	$127.41	$127.40	$127.40
Purchase #5	$246.47	13.393%	$279.4797	$279.48	$279.50	$279.50
Purchase #6	$68.33	8.771%	$74.3232	$74.32	$74.30	$74.30
Purchase #7	$82.45	12.541%	$92.7901	$92.79	$92.80	$92.80
7 purchase totals =	$730.67		$809.0336	$809.03	$809.00	$809.10