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	$61.37	6.389%	$65.2909	$65.29	$65.30	$65.30
Purchase #2	$226.81	12.485%	$255.1272	$255.13	$255.15	$255.10
Purchase #3	$119.45	11.533%	$133.2262	$133.23	$133.25	$133.20
Purchase #4	$88.85	13.553%	$100.8918	$100.89	$100.90	$100.90
Purchase #5	$160.76	13.552%	$182.5462	$182.55	$182.55	$182.50
Purchase #6	$144.59	4.872%	$151.6344	$151.63	$151.65	$151.60
Purchase #7	$12.42	11.655%	$13.8676	$13.87	$13.85	$13.90
7 purchase totals =	$814.25		$902.5843	$902.59	$902.65	$902.50