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	$134.83	10.393%	$148.8429	$148.84	$148.85	$148.80
Purchase #2	$135.75	4.390%	$141.7094	$141.71	$141.70	$141.70
Purchase #3	$238.51	4.833%	$250.0372	$250.04	$250.05	$250.00
Purchase #4	$10.82	10.577%	$11.9644	$11.96	$11.95	$12.00
Purchase #5	$73.35	12.853%	$82.7777	$82.78	$82.80	$82.80
Purchase #6	$173.90	10.553%	$192.2517	$192.25	$192.25	$192.30
Purchase #7	$179.96	5.629%	$190.0899	$190.09	$190.10	$190.10
7 purchase totals =	$947.12		$1,017.6732	$1,017.67	$1,017.70	$1,017.70