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	$225.40	13.397%	$255.5968	$255.60	$255.60	$255.60
Purchase #2	$55.39	7.844%	$59.7348	$59.73	$59.75	$59.70
Purchase #3	$241.68	12.504%	$271.8997	$271.90	$271.90	$271.90
Purchase #4	$129.81	9.316%	$141.9031	$141.90	$141.90	$141.90
Purchase #5	$198.98	12.591%	$224.0336	$224.03	$224.05	$224.00
Purchase #6	$149.26	3.766%	$154.8811	$154.88	$154.90	$154.90
Purchase #7	$167.94	13.690%	$190.931	$190.93	$190.95	$190.90
7 purchase totals =	$1,168.46		$1,298.9801	$1,298.97	$1,299.05	$1,298.90