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	$170.83	11.643%	$190.7197	$190.72	$190.70	$190.70
Purchase #2	$41.53	3.330%	$42.9129	$42.91	$42.90	$42.90
Purchase #3	$155.88	9.350%	$170.4548	$170.45	$170.45	$170.50
Purchase #4	$142.77	13.788%	$162.4551	$162.46	$162.45	$162.50
Purchase #5	$221.73	11.325%	$246.8409	$246.84	$246.85	$246.80
Purchase #6	$126.45	13.678%	$143.7458	$143.75	$143.75	$143.70
Purchase #7	$42.86	12.493%	$48.2145	$48.21	$48.20	$48.20
7 purchase totals =	$902.05		$1,005.3437	$1,005.34	$1,005.30	$1,005.30