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	$241.58	6.184%	$256.5193	$256.52	$256.50	$256.50
Purchase #2	$40.89	6.405%	$43.509	$43.51	$43.50	$43.50
Purchase #3	$225.89	5.775%	$238.9351	$238.94	$238.95	$238.90
Purchase #4	$45.39	13.846%	$51.6747	$51.67	$51.65	$51.70
Purchase #5	$80.44	12.151%	$90.2143	$90.21	$90.20	$90.20
Purchase #6	$13.57	12.696%	$15.2928	$15.29	$15.30	$15.30
Purchase #7	$212.43	6.715%	$226.6947	$226.69	$226.70	$226.70
7 purchase totals =	$860.19		$922.8399	$922.83	$922.80	$922.80