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	$237.95	7.383%	$255.5178	$255.52	$255.50	$255.50
Purchase #2	$149.37	10.372%	$164.8627	$164.86	$164.85	$164.90
Purchase #3	$157.39	4.516%	$164.4977	$164.50	$164.50	$164.50
Purchase #4	$244.98	12.193%	$274.8504	$274.85	$274.85	$274.90
Purchase #5	$107.85	4.851%	$113.0818	$113.08	$113.10	$113.10
Purchase #6	$161.62	13.732%	$183.8137	$183.81	$183.80	$183.80
Purchase #7	$54.67	11.252%	$60.8215	$60.82	$60.80	$60.80
7 purchase totals =	$1,113.83		$1,217.4456	$1,217.44	$1,217.40	$1,217.50