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	$226.87	12.526%	$255.2877	$255.29	$255.30	$255.30
Purchase #2	$41.30	4.285%	$43.0697	$43.07	$43.05	$43.10
Purchase #3	$205.90	4.839%	$215.8635	$215.86	$215.85	$215.90
Purchase #4	$30.40	3.107%	$31.3445	$31.34	$31.35	$31.30
Purchase #5	$15.94	12.408%	$17.9178	$17.92	$17.90	$17.90
Purchase #6	$242.71	10.221%	$267.5174	$267.52	$267.50	$267.50
Purchase #7	$65.82	13.173%	$74.4905	$74.49	$74.50	$74.50
7 purchase totals =	$828.94		$905.4911	$905.49	$905.45	$905.50