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	$136.46	5.856%	$144.4511	$144.45	$144.45	$144.50
Purchase #2	$64.67	13.833%	$73.6158	$73.62	$73.60	$73.60
Purchase #3	$205.80	7.348%	$220.9222	$220.92	$220.90	$220.90
Purchase #4	$244.28	11.149%	$271.5148	$271.51	$271.50	$271.50
Purchase #5	$158.84	8.617%	$172.5272	$172.53	$172.55	$172.50
Purchase #6	$126.77	3.848%	$131.6481	$131.65	$131.65	$131.60
Purchase #7	$114.69	7.438%	$123.2206	$123.22	$123.20	$123.20
7 purchase totals =	$1,051.51		$1,137.8998	$1,137.90	$1,137.85	$1,137.80