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	$21.89	13.682%	$24.885	$24.89	$24.90	$24.90
Purchase #2	$129.88	7.162%	$139.182	$139.18	$139.20	$139.20
Purchase #3	$173.70	9.112%	$189.5275	$189.53	$189.55	$189.50
Purchase #4	$191.91	4.711%	$200.9509	$200.95	$200.95	$201.00
Purchase #5	$46.65	11.325%	$51.9331	$51.93	$51.95	$51.90
Purchase #6	$142.68	10.773%	$158.0509	$158.05	$158.05	$158.10
Purchase #7	$87.83	13.299%	$99.5105	$99.51	$99.50	$99.50
7 purchase totals =	$794.54		$864.0399	$864.04	$864.10	$864.10