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	$27.97	6.867%	$29.8907	$29.89	$29.90	$29.90
Purchase #2	$220.83	3.499%	$228.5568	$228.56	$228.55	$228.60
Purchase #3	$100.83	7.870%	$108.7653	$108.77	$108.75	$108.80
Purchase #4	$59.60	9.126%	$65.0391	$65.04	$65.05	$65.00
Purchase #5	$54.53	13.867%	$62.0917	$62.09	$62.10	$62.10
Purchase #6	$143.30	8.698%	$155.7642	$155.76	$155.75	$155.80
Purchase #7	$154.56	6.438%	$164.5106	$164.51	$164.50	$164.50
7 purchase totals =	$761.62		$814.6184	$814.62	$814.60	$814.70