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	$241.69	6.737%	$257.9727	$257.97	$257.95	$258.00
Purchase #2	$18.74	12.563%	$21.0943	$21.09	$21.10	$21.10
Purchase #3	$74.25	6.814%	$79.3094	$79.31	$79.30	$79.30
Purchase #4	$123.26	13.151%	$139.4699	$139.47	$139.45	$139.50
Purchase #5	$205.93	7.872%	$222.1408	$222.14	$222.15	$222.10
Purchase #6	$102.38	9.247%	$111.8471	$111.85	$111.85	$111.80
Purchase #7	$67.83	10.308%	$74.8219	$74.82	$74.80	$74.80
7 purchase totals =	$834.08		$906.6561	$906.65	$906.60	$906.60