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	$200.84	10.340%	$221.6069	$221.61	$221.60	$221.60
Purchase #2	$125.63	5.149%	$132.0987	$132.10	$132.10	$132.10
Purchase #3	$109.47	9.617%	$119.9977	$120.00	$120.00	$120.00
Purchase #4	$137.98	12.404%	$155.095	$155.10	$155.10	$155.10
Purchase #5	$145.81	4.514%	$152.3919	$152.39	$152.40	$152.40
Purchase #6	$171.47	10.622%	$189.6835	$189.68	$189.70	$189.70
Purchase #7	$6.67	10.310%	$7.3577	$7.36	$7.35	$7.40
7 purchase totals =	$897.87		$978.2314	$978.24	$978.25	$978.30