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	$107.31	13.505%	$121.8022	$121.80	$121.80	$121.80
Purchase #2	$78.37	12.720%	$88.3387	$88.34	$88.35	$88.30
Purchase #3	$160.68	9.163%	$175.4031	$175.40	$175.40	$175.40
Purchase #4	$128.40	3.196%	$132.5037	$132.50	$132.50	$132.50
Purchase #5	$82.75	9.794%	$90.8545	$90.85	$90.85	$90.90
Purchase #6	$85.99	5.248%	$90.5028	$90.50	$90.50	$90.50
Purchase #7	$41.31	4.762%	$43.2772	$43.28	$43.30	$43.30
7 purchase totals =	$684.81		$742.6822	$742.67	$742.70	$742.70