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	$159.98	5.501%	$168.7805	$168.78	$168.80	$168.80
Purchase #2	$84.27	3.857%	$87.5203	$87.52	$87.50	$87.50
Purchase #3	$94.61	7.629%	$101.8278	$101.83	$101.85	$101.80
Purchase #4	$159.92	11.600%	$178.4707	$178.47	$178.45	$178.50
Purchase #5	$217.67	9.736%	$238.8624	$238.86	$238.85	$238.90
Purchase #6	$198.77	11.175%	$220.9825	$220.98	$221.00	$221.00
Purchase #7	$20.68	3.350%	$21.3728	$21.37	$21.35	$21.40
7 purchase totals =	$935.90		$1,017.8170	$1,017.81	$1,017.80	$1,017.90