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	$18.64	10.548%	$20.6061	$20.61	$20.60	$20.60
Purchase #2	$43.48	10.132%	$47.8854	$47.89	$47.90	$47.90
Purchase #3	$29.45	4.835%	$30.8739	$30.87	$30.85	$30.90
Purchase #4	$65.43	6.631%	$69.7687	$69.77	$69.75	$69.80
Purchase #5	$90.37	13.587%	$102.6486	$102.65	$102.65	$102.60
Purchase #6	$132.75	6.667%	$141.6004	$141.60	$141.60	$141.60
Purchase #7	$108.31	5.638%	$114.4165	$114.42	$114.40	$114.40
7 purchase totals =	$488.43		$527.7996	$527.81	$527.75	$527.80