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	$18.31	12.724%	$20.6398	$20.64	$20.65	$20.60
Purchase #2	$91.75	4.210%	$95.6127	$95.61	$95.60	$95.60
Purchase #3	$20.84	5.292%	$21.9429	$21.94	$21.95	$21.90
Purchase #4	$176.54	7.363%	$189.5386	$189.54	$189.55	$189.50
Purchase #5	$156.63	6.666%	$167.071	$167.07	$167.05	$167.10
Purchase #6	$176.78	5.563%	$186.6143	$186.61	$186.60	$186.60
Purchase #7	$46.61	5.319%	$49.0892	$49.09	$49.10	$49.10
7 purchase totals =	$687.46		$730.5085	$730.50	$730.50	$730.40