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	$226.49	12.604%	$255.0368	$255.04	$255.05	$255.00
Purchase #2	$196.26	9.791%	$215.4758	$215.48	$215.50	$215.50
Purchase #3	$17.37	3.581%	$17.992	$17.99	$18.00	$18.00
Purchase #4	$41.55	10.360%	$45.8546	$45.85	$45.85	$45.90
Purchase #5	$163.96	5.522%	$173.0139	$173.01	$173.00	$173.00
Purchase #6	$32.70	3.760%	$33.9295	$33.93	$33.95	$33.90
Purchase #7	$40.48	10.505%	$44.7324	$44.73	$44.75	$44.70
7 purchase totals =	$718.81		$786.0350	$786.03	$786.10	$786.00