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	$109.84	11.708%	$122.7001	$122.70	$122.70	$122.70
Purchase #2	$100.86	3.214%	$104.1016	$104.10	$104.10	$104.10
Purchase #3	$114.66	6.311%	$121.8962	$121.90	$121.90	$121.90
Purchase #4	$143.65	4.460%	$150.0568	$150.06	$150.05	$150.10
Purchase #5	$41.32	4.759%	$43.2864	$43.29	$43.30	$43.30
Purchase #6	$86.83	4.357%	$90.6132	$90.61	$90.60	$90.60
Purchase #7	$124.34	11.400%	$138.5148	$138.51	$138.50	$138.50
7 purchase totals =	$721.50		$771.1691	$771.17	$771.15	$771.20