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	$66.98	4.359%	$69.8997	$69.90	$69.90	$69.90
Purchase #2	$15.66	11.106%	$17.3992	$17.40	$17.40	$17.40
Purchase #3	$39.41	11.342%	$43.8799	$43.88	$43.90	$43.90
Purchase #4	$143.90	9.636%	$157.7662	$157.77	$157.75	$157.80
Purchase #5	$224.31	13.690%	$255.018	$255.02	$255.00	$255.00
Purchase #6	$105.84	7.767%	$114.0606	$114.06	$114.05	$114.10
Purchase #7	$171.68	11.476%	$191.382	$191.38	$191.40	$191.40
7 purchase totals =	$767.78		$849.4056	$849.41	$849.40	$849.50