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	$62.70	6.536%	$66.7981	$66.80	$66.80	$66.80
Purchase #2	$12.86	7.195%	$13.7853	$13.79	$13.80	$13.80
Purchase #3	$102.82	13.306%	$116.5012	$116.50	$116.50	$116.50
Purchase #4	$73.78	6.309%	$78.4348	$78.43	$78.45	$78.40
Purchase #5	$180.33	6.388%	$191.8495	$191.85	$191.85	$191.80
Purchase #6	$63.79	9.665%	$69.9553	$69.96	$69.95	$70.00
Purchase #7	$166.74	8.816%	$181.4398	$181.44	$181.45	$181.40
7 purchase totals =	$663.02		$718.7640	$718.77	$718.80	$718.70