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	$112.97	6.119%	$119.8826	$119.88	$119.90	$119.90
Purchase #2	$83.59	13.690%	$95.0335	$95.03	$95.05	$95.00
Purchase #3	$53.94	13.202%	$61.0612	$61.06	$61.05	$61.10
Purchase #4	$223.99	5.570%	$236.4662	$236.47	$236.45	$236.50
Purchase #5	$194.82	11.583%	$217.386	$217.39	$217.40	$217.40
Purchase #6	$51.83	5.726%	$54.7978	$54.80	$54.80	$54.80
Purchase #7	$118.51	11.275%	$131.872	$131.87	$131.85	$131.90
7 purchase totals =	$839.65		$916.4993	$916.50	$916.50	$916.60