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	$225.75	13.750%	$256.7906	$256.79	$256.80	$256.80
Purchase #2	$237.77	3.285%	$245.5807	$245.58	$245.60	$245.60
Purchase #3	$20.54	6.165%	$21.8063	$21.81	$21.80	$21.80
Purchase #4	$108.50	9.508%	$118.8162	$118.82	$118.80	$118.80
Purchase #5	$60.53	9.250%	$66.129	$66.13	$66.15	$66.10
Purchase #6	$207.89	12.431%	$233.7328	$233.73	$233.75	$233.70
Purchase #7	$140.75	12.205%	$157.9285	$157.93	$157.95	$157.90
7 purchase totals =	$1,001.73		$1,100.7841	$1,100.79	$1,100.85	$1,100.70