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	$97.71	13.635%	$111.0328	$111.03	$111.05	$111.00
Purchase #2	$11.47	12.383%	$12.8903	$12.89	$12.90	$12.90
Purchase #3	$205.34	12.442%	$230.8884	$230.89	$230.90	$230.90
Purchase #4	$110.58	3.311%	$114.2413	$114.24	$114.25	$114.20
Purchase #5	$119.84	12.536%	$134.8631	$134.86	$134.85	$134.90
Purchase #6	$83.64	7.245%	$89.6997	$89.70	$89.70	$89.70
Purchase #7	$181.48	3.482%	$187.7991	$187.80	$187.80	$187.80
7 purchase totals =	$810.06		$881.4147	$881.41	$881.45	$881.40