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	$73.84	6.826%	$78.8803	$78.88	$78.90	$78.90
Purchase #2	$199.48	11.724%	$222.867	$222.87	$222.85	$222.90
Purchase #3	$20.86	5.819%	$22.0738	$22.07	$22.05	$22.10
Purchase #4	$192.67	3.325%	$199.0763	$199.08	$199.10	$199.10
Purchase #5	$165.60	3.433%	$171.285	$171.29	$171.30	$171.30
Purchase #6	$121.93	12.832%	$137.5761	$137.58	$137.60	$137.60
Purchase #7	$47.57	5.723%	$50.2924	$50.29	$50.30	$50.30
7 purchase totals =	$821.95		$882.0509	$882.06	$882.10	$882.20