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	$135.77	6.656%	$144.8069	$144.81	$144.80	$144.80
Purchase #2	$52.57	10.181%	$57.9222	$57.92	$57.90	$57.90
Purchase #3	$167.37	12.106%	$187.6318	$187.63	$187.65	$187.60
Purchase #4	$138.98	4.737%	$145.5635	$145.56	$145.55	$145.60
Purchase #5	$250.83	6.548%	$267.2543	$267.25	$267.25	$267.30
Purchase #6	$106.27	11.857%	$118.8704	$118.87	$118.85	$118.90
Purchase #7	$110.83	8.118%	$119.8272	$119.83	$119.85	$119.80
7 purchase totals =	$962.62		$1,041.8763	$1,041.87	$1,041.85	$1,041.90