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	$86.33	3.688%	$89.5139	$89.51	$89.50	$89.50
Purchase #2	$50.29	9.304%	$54.969	$54.97	$54.95	$55.00
Purchase #3	$203.47	10.273%	$224.3725	$224.37	$224.35	$224.40
Purchase #4	$82.55	5.434%	$87.0358	$87.04	$87.05	$87.00
Purchase #5	$222.43	12.116%	$249.3796	$249.38	$249.40	$249.40
Purchase #6	$194.66	5.501%	$205.3682	$205.37	$205.35	$205.40
Purchase #7	$169.40	4.272%	$176.6368	$176.64	$176.65	$176.60
7 purchase totals =	$1,009.13		$1,087.2758	$1,087.28	$1,087.25	$1,087.30