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	$11.93	10.412%	$13.1722	$13.17	$13.15	$13.20
Purchase #2	$129.34	8.564%	$140.4167	$140.42	$140.40	$140.40
Purchase #3	$117.95	4.459%	$123.2094	$123.21	$123.20	$123.20
Purchase #4	$37.99	5.582%	$40.1106	$40.11	$40.10	$40.10
Purchase #5	$203.39	4.808%	$213.169	$213.17	$213.15	$213.20
Purchase #6	$43.45	4.807%	$45.5386	$45.54	$45.55	$45.50
Purchase #7	$105.32	12.456%	$118.4387	$118.44	$118.45	$118.40
7 purchase totals =	$649.37		$694.0552	$694.06	$694.00	$694.00