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	$45.63	13.186%	$51.6468	$51.65	$51.65	$51.60
Purchase #2	$52.32	13.489%	$59.3774	$59.38	$59.40	$59.40
Purchase #3	$143.52	5.405%	$151.2773	$151.28	$151.30	$151.30
Purchase #4	$112.78	11.481%	$125.7283	$125.73	$125.75	$125.70
Purchase #5	$41.91	3.797%	$43.5013	$43.50	$43.50	$43.50
Purchase #6	$122.31	7.494%	$131.4759	$131.48	$131.50	$131.50
Purchase #7	$39.99	7.545%	$43.0072	$43.01	$43.00	$43.00
7 purchase totals =	$558.46		$606.0142	$606.03	$606.10	$606.00