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	$28.44	9.613%	$31.1739	$31.17	$31.15	$31.20
Purchase #2	$100.97	4.598%	$105.6126	$105.61	$105.60	$105.60
Purchase #3	$134.75	3.171%	$139.0229	$139.02	$139.00	$139.00
Purchase #4	$105.57	13.195%	$119.5	$119.50	$119.50	$119.50
Purchase #5	$80.41	6.249%	$85.4348	$85.43	$85.45	$85.40
Purchase #6	$125.85	12.367%	$141.4139	$141.41	$141.40	$141.40
Purchase #7	$118.63	12.838%	$133.8597	$133.86	$133.85	$133.90
7 purchase totals =	$694.62		$756.0178	$756.00	$755.95	$756.00