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	$144.66	13.508%	$164.2007	$164.20	$164.20	$164.20
Purchase #2	$226.67	3.184%	$233.8872	$233.89	$233.90	$233.90
Purchase #3	$141.83	10.566%	$156.8158	$156.82	$156.80	$156.80
Purchase #4	$41.68	3.821%	$43.2726	$43.27	$43.25	$43.30
Purchase #5	$160.45	4.186%	$167.1664	$167.17	$167.15	$167.20
Purchase #6	$135.58	5.497%	$143.0328	$143.03	$143.05	$143.00
Purchase #7	$39.72	4.541%	$41.5237	$41.52	$41.50	$41.50
7 purchase totals =	$890.59		$949.8992	$949.90	$949.85	$949.90