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	$20.31	10.706%	$22.4844	$22.48	$22.50	$22.50
Purchase #2	$172.50	12.772%	$194.5317	$194.53	$194.55	$194.50
Purchase #3	$52.97	3.324%	$54.7307	$54.73	$54.75	$54.70
Purchase #4	$233.76	3.149%	$241.1211	$241.12	$241.10	$241.10
Purchase #5	$228.67	13.853%	$260.3477	$260.35	$260.35	$260.30
Purchase #6	$43.71	12.853%	$49.328	$49.33	$49.35	$49.30
Purchase #7	$65.58	11.106%	$72.8633	$72.86	$72.85	$72.90
7 purchase totals =	$817.50		$895.4069	$895.40	$895.45	$895.30