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	$21.93	11.792%	$24.516	$24.52	$24.50	$24.50
Purchase #2	$59.78	4.492%	$62.4653	$62.47	$62.45	$62.50
Purchase #3	$168.40	10.226%	$185.6206	$185.62	$185.60	$185.60
Purchase #4	$39.51	10.189%	$43.5357	$43.54	$43.55	$43.50
Purchase #5	$224.56	6.131%	$238.3278	$238.33	$238.35	$238.30
Purchase #6	$132.88	7.529%	$142.8845	$142.88	$142.90	$142.90
Purchase #7	$70.91	7.271%	$76.0659	$76.07	$76.05	$76.10
7 purchase totals =	$717.97		$773.4158	$773.43	$773.40	$773.40