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	$249.87	12.296%	$280.594	$280.59	$280.60	$280.60
Purchase #2	$242.46	13.632%	$275.5121	$275.51	$275.50	$275.50
Purchase #3	$107.74	3.212%	$111.2006	$111.20	$111.20	$111.20
Purchase #4	$38.87	8.567%	$42.2	$42.20	$42.20	$42.20
Purchase #5	$8.25	4.122%	$8.5901	$8.59	$8.60	$8.60
Purchase #6	$134.26	6.467%	$142.9426	$142.94	$142.95	$142.90
Purchase #7	$170.94	11.634%	$190.8272	$190.83	$190.85	$190.80
7 purchase totals =	$952.39		$1,051.8666	$1,051.86	$1,051.90	$1,051.80