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	$103.53	13.571%	$117.5801	$117.58	$117.60	$117.60
Purchase #2	$83.70	9.313%	$91.495	$91.50	$91.50	$91.50
Purchase #3	$184.96	4.303%	$192.9188	$192.92	$192.90	$192.90
Purchase #4	$126.40	3.477%	$130.7949	$130.79	$130.80	$130.80
Purchase #5	$120.64	5.175%	$126.8831	$126.88	$126.90	$126.90
Purchase #6	$16.86	9.789%	$18.5104	$18.51	$18.50	$18.50
Purchase #7	$125.82	13.273%	$142.5201	$142.52	$142.50	$142.50
7 purchase totals =	$761.91		$820.7024	$820.70	$820.70	$820.70