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	$129.63	5.665%	$136.9735	$136.97	$136.95	$137.00
Purchase #2	$73.56	12.453%	$82.7204	$82.72	$82.70	$82.70
Purchase #3	$215.97	11.675%	$241.1845	$241.18	$241.20	$241.20
Purchase #4	$196.86	12.509%	$221.4852	$221.49	$221.50	$221.50
Purchase #5	$75.83	8.187%	$82.0382	$82.04	$82.05	$82.00
Purchase #6	$174.52	12.184%	$195.7835	$195.78	$195.80	$195.80
Purchase #7	$66.78	9.166%	$72.9011	$72.90	$72.90	$72.90
7 purchase totals =	$933.15		$1,033.0864	$1,033.08	$1,033.10	$1,033.10