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	$10.88	6.387%	$11.5749	$11.57	$11.55	$11.60
Purchase #2	$111.73	10.547%	$123.5142	$123.51	$123.50	$123.50
Purchase #3	$34.73	12.191%	$38.9639	$38.96	$38.95	$39.00
Purchase #4	$156.72	9.258%	$171.2291	$171.23	$171.25	$171.20
Purchase #5	$207.45	12.773%	$233.9476	$233.95	$233.95	$233.90
Purchase #6	$36.64	11.221%	$40.7514	$40.75	$40.75	$40.80
Purchase #7	$122.78	3.138%	$126.6328	$126.63	$126.65	$126.60
7 purchase totals =	$680.93		$746.6139	$746.60	$746.60	$746.60