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	$91.28	9.662%	$100.0995	$100.10	$100.10	$100.10
Purchase #2	$137.31	4.271%	$143.1745	$143.17	$143.15	$143.20
Purchase #3	$22.89	12.255%	$25.6952	$25.70	$25.70	$25.70
Purchase #4	$166.60	3.410%	$172.2811	$172.28	$172.30	$172.30
Purchase #5	$140.69	8.433%	$152.5544	$152.55	$152.55	$152.60
Purchase #6	$23.72	4.713%	$24.8379	$24.84	$24.85	$24.80
Purchase #7	$241.94	8.638%	$262.8388	$262.84	$262.85	$262.80
7 purchase totals =	$824.43		$881.4814	$881.48	$881.50	$881.50