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	$177.78	6.734%	$189.7517	$189.75	$189.75	$189.80
Purchase #2	$142.32	8.215%	$154.0116	$154.01	$154.00	$154.00
Purchase #3	$236.66	7.660%	$254.7882	$254.79	$254.80	$254.80
Purchase #4	$51.45	11.364%	$57.2968	$57.30	$57.30	$57.30
Purchase #5	$126.39	4.668%	$132.2899	$132.29	$132.30	$132.30
Purchase #6	$127.41	11.811%	$142.4584	$142.46	$142.45	$142.50
Purchase #7	$105.40	12.763%	$118.8522	$118.85	$118.85	$118.90
7 purchase totals =	$967.41		$1,049.4488	$1,049.45	$1,049.45	$1,049.60