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	$46.38	10.178%	$51.1006	$51.10	$51.10	$51.10
Purchase #2	$39.83	7.524%	$42.8268	$42.83	$42.85	$42.80
Purchase #3	$225.28	13.867%	$256.5196	$256.52	$256.50	$256.50
Purchase #4	$66.69	6.866%	$71.2689	$71.27	$71.25	$71.30
Purchase #5	$119.91	4.551%	$125.3671	$125.37	$125.35	$125.40
Purchase #6	$171.66	7.147%	$183.9285	$183.93	$183.95	$183.90
Purchase #7	$136.72	5.768%	$144.606	$144.61	$144.60	$144.60
7 purchase totals =	$806.47		$875.6175	$875.63	$875.60	$875.60