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	$39.68	3.285%	$40.9835	$40.98	$41.00	$41.00
Purchase #2	$136.90	4.324%	$142.8196	$142.82	$142.80	$142.80
Purchase #3	$182.54	6.247%	$193.9433	$193.94	$193.95	$193.90
Purchase #4	$90.41	10.685%	$100.0703	$100.07	$100.05	$100.10
Purchase #5	$29.45	7.600%	$31.6882	$31.69	$31.70	$31.70
Purchase #6	$18.55	12.207%	$20.8144	$20.81	$20.80	$20.80
Purchase #7	$118.83	10.796%	$131.6589	$131.66	$131.65	$131.70
7 purchase totals =	$616.36		$661.9782	$661.97	$661.95	$662.00