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	$49.96	8.675%	$54.294	$54.29	$54.30	$54.30
Purchase #2	$201.50	7.800%	$217.217	$217.22	$217.20	$217.20
Purchase #3	$217.54	11.423%	$242.3896	$242.39	$242.40	$242.40
Purchase #4	$40.67	10.234%	$44.8322	$44.83	$44.85	$44.80
Purchase #5	$236.78	10.866%	$262.5085	$262.51	$262.50	$262.50
Purchase #6	$41.79	4.823%	$43.8055	$43.81	$43.80	$43.80
Purchase #7	$68.52	5.703%	$72.4277	$72.43	$72.45	$72.40
7 purchase totals =	$856.76		$937.4745	$937.48	$937.50	$937.40