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	$241.97	4.352%	$252.5005	$252.50	$252.50	$252.50
Purchase #2	$153.52	5.722%	$162.3044	$162.30	$162.30	$162.30
Purchase #3	$103.61	12.202%	$116.2525	$116.25	$116.25	$116.30
Purchase #4	$101.53	4.329%	$105.9252	$105.93	$105.95	$105.90
Purchase #5	$59.35	4.547%	$62.0486	$62.05	$62.05	$62.00
Purchase #6	$161.62	10.334%	$178.3218	$178.32	$178.30	$178.30
Purchase #7	$144.25	12.641%	$162.4846	$162.48	$162.50	$162.50
7 purchase totals =	$965.85		$1,039.8376	$1,039.83	$1,039.85	$1,039.80