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	$37.72	10.785%	$41.7881	$41.79	$41.80	$41.80
Purchase #2	$120.37	9.535%	$131.8473	$131.85	$131.85	$131.80
Purchase #3	$57.67	10.607%	$63.7871	$63.79	$63.80	$63.80
Purchase #4	$206.37	13.504%	$234.2382	$234.24	$234.25	$234.20
Purchase #5	$127.43	13.412%	$144.5209	$144.52	$144.50	$144.50
Purchase #6	$213.66	5.243%	$224.8622	$224.86	$224.85	$224.90
Purchase #7	$106.68	4.425%	$111.4006	$111.40	$111.40	$111.40
7 purchase totals =	$869.90		$952.4444	$952.45	$952.45	$952.40