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	$62.68	6.724%	$66.8946	$66.89	$66.90	$66.90
Purchase #2	$119.40	11.636%	$133.2934	$133.29	$133.30	$133.30
Purchase #3	$54.85	8.555%	$59.5424	$59.54	$59.55	$59.50
Purchase #4	$12.89	5.775%	$13.6344	$13.63	$13.65	$13.60
Purchase #5	$246.71	4.153%	$256.9559	$256.96	$256.95	$257.00
Purchase #6	$82.82	9.136%	$90.3864	$90.39	$90.40	$90.40
Purchase #7	$67.86	4.274%	$70.7603	$70.76	$70.75	$70.80
7 purchase totals =	$647.21		$691.4674	$691.46	$691.50	$691.50