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	$13.53	9.176%	$14.7715	$14.77	$14.75	$14.80
Purchase #2	$139.93	13.547%	$158.8863	$158.89	$158.90	$158.90
Purchase #3	$228.29	11.550%	$254.6575	$254.66	$254.65	$254.70
Purchase #4	$151.83	11.770%	$169.7004	$169.70	$169.70	$169.70
Purchase #5	$70.58	3.272%	$72.8894	$72.89	$72.90	$72.90
Purchase #6	$68.62	12.737%	$77.3601	$77.36	$77.35	$77.40
Purchase #7	$176.85	4.621%	$185.0222	$185.02	$185.00	$185.00
7 purchase totals =	$849.63		$933.2874	$933.29	$933.25	$933.40