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	$241.53	5.818%	$255.5822	$255.58	$255.60	$255.60
Purchase #2	$107.56	3.699%	$111.5386	$111.54	$111.55	$111.50
Purchase #3	$143.85	10.863%	$159.4764	$159.48	$159.50	$159.50
Purchase #4	$120.63	13.120%	$136.4567	$136.46	$136.45	$136.50
Purchase #5	$189.60	4.856%	$198.807	$198.81	$198.80	$198.80
Purchase #6	$107.79	9.574%	$118.1098	$118.11	$118.10	$118.10
Purchase #7	$250.42	7.832%	$270.0329	$270.03	$270.05	$270.00
7 purchase totals =	$1,161.38		$1,250.0036	$1,250.01	$1,250.05	$1,250.00