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	$154.73	11.436%	$172.4249	$172.42	$172.40	$172.40
Purchase #2	$219.86	12.269%	$246.8346	$246.83	$246.85	$246.80
Purchase #3	$158.72	3.798%	$164.7482	$164.75	$164.75	$164.70
Purchase #4	$196.99	11.649%	$219.9374	$219.94	$219.95	$219.90
Purchase #5	$43.36	10.311%	$47.8308	$47.83	$47.85	$47.80
Purchase #6	$77.60	11.857%	$86.801	$86.80	$86.80	$86.80
Purchase #7	$83.35	7.833%	$89.8788	$89.88	$89.90	$89.90
7 purchase totals =	$934.61		$1,028.4557	$1,028.45	$1,028.50	$1,028.30