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	$135.36	3.127%	$139.5927	$139.59	$139.60	$139.60
Purchase #2	$6.37	7.135%	$6.8245	$6.82	$6.80	$6.80
Purchase #3	$73.48	4.844%	$77.0394	$77.04	$77.05	$77.00
Purchase #4	$161.36	7.553%	$173.5475	$173.55	$173.55	$173.50
Purchase #5	$137.32	5.246%	$144.5238	$144.52	$144.50	$144.50
Purchase #6	$38.31	6.727%	$40.8871	$40.89	$40.90	$40.90
Purchase #7	$38.83	7.663%	$41.8055	$41.81	$41.80	$41.80
7 purchase totals =	$591.03		$624.2205	$624.22	$624.20	$624.10