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	$179.84	7.404%	$193.1554	$193.16	$193.15	$193.20
Purchase #2	$144.60	10.671%	$160.0303	$160.03	$160.05	$160.00
Purchase #3	$172.33	7.186%	$184.7136	$184.71	$184.70	$184.70
Purchase #4	$123.83	11.309%	$137.8339	$137.83	$137.85	$137.80
Purchase #5	$126.48	13.734%	$143.8508	$143.85	$143.85	$143.90
Purchase #6	$160.83	10.585%	$177.8539	$177.85	$177.85	$177.90
Purchase #7	$80.45	10.105%	$88.5795	$88.58	$88.60	$88.60
7 purchase totals =	$988.36		$1,086.0174	$1,086.01	$1,086.05	$1,086.10