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	$76.82	7.243%	$82.3841	$82.38	$82.40	$82.40
Purchase #2	$123.41	6.378%	$131.2811	$131.28	$131.30	$131.30
Purchase #3	$105.26	7.801%	$113.4713	$113.47	$113.45	$113.50
Purchase #4	$238.87	3.351%	$246.8745	$246.87	$246.85	$246.90
Purchase #5	$34.31	13.456%	$38.9268	$38.93	$38.95	$38.90
Purchase #6	$57.25	5.708%	$60.5178	$60.52	$60.50	$60.50
Purchase #7	$15.30	11.564%	$17.0693	$17.07	$17.05	$17.10
7 purchase totals =	$651.22		$690.5249	$690.52	$690.50	$690.60