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	$137.74	4.150%	$143.4562	$143.46	$143.45	$143.50
Purchase #2	$185.42	7.189%	$198.7498	$198.75	$198.75	$198.70
Purchase #3	$112.71	13.584%	$128.0205	$128.02	$128.00	$128.00
Purchase #4	$246.29	6.615%	$262.5821	$262.58	$262.60	$262.60
Purchase #5	$66.41	3.170%	$68.5152	$68.52	$68.50	$68.50
Purchase #6	$38.69	9.539%	$42.3806	$42.38	$42.40	$42.40
Purchase #7	$126.91	8.423%	$137.5996	$137.60	$137.60	$137.60
7 purchase totals =	$914.17		$981.3040	$981.31	$981.30	$981.30