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	$215.60	6.147%	$228.8529	$228.85	$228.85	$228.90
Purchase #2	$236.58	10.295%	$260.9359	$260.94	$260.95	$260.90
Purchase #3	$250.80	11.636%	$279.9831	$279.98	$280.00	$280.00
Purchase #4	$59.94	11.345%	$66.7402	$66.74	$66.75	$66.70
Purchase #5	$105.46	11.784%	$117.8874	$117.89	$117.90	$117.90
Purchase #6	$164.75	4.401%	$172.0006	$172.00	$172.00	$172.00
Purchase #7	$157.93	8.480%	$171.3225	$171.32	$171.30	$171.30
7 purchase totals =	$1,191.06		$1,297.7226	$1,297.72	$1,297.75	$1,297.70