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	$144.92	10.803%	$160.5757	$160.58	$160.60	$160.60
Purchase #2	$136.71	7.105%	$146.4232	$146.42	$146.40	$146.40
Purchase #3	$81.46	12.643%	$91.759	$91.76	$91.75	$91.80
Purchase #4	$131.83	8.421%	$142.9314	$142.93	$142.95	$142.90
Purchase #5	$77.73	6.678%	$82.9208	$82.92	$82.90	$82.90
Purchase #6	$92.28	9.498%	$101.0448	$101.04	$101.05	$101.00
Purchase #7	$112.72	4.627%	$117.9356	$117.94	$117.95	$117.90
7 purchase totals =	$777.65		$843.5905	$843.59	$843.60	$843.50