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	$242.50	7.225%	$260.0206	$260.02	$260.00	$260.00
Purchase #2	$135.70	6.729%	$144.8313	$144.83	$144.85	$144.80
Purchase #3	$56.30	12.704%	$63.4524	$63.45	$63.45	$63.50
Purchase #4	$39.32	6.391%	$41.8329	$41.83	$41.85	$41.80
Purchase #5	$156.68	10.533%	$173.1831	$173.18	$173.20	$173.20
Purchase #6	$67.30	8.260%	$72.859	$72.86	$72.85	$72.90
Purchase #7	$219.55	6.280%	$233.3377	$233.34	$233.35	$233.30
7 purchase totals =	$917.35		$989.5170	$989.51	$989.55	$989.50