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	$130.60	11.627%	$145.7849	$145.78	$145.80	$145.80
Purchase #2	$78.86	12.350%	$88.5992	$88.60	$88.60	$88.60
Purchase #3	$127.73	7.268%	$137.0134	$137.01	$137.00	$137.00
Purchase #4	$116.94	5.778%	$123.6968	$123.70	$123.70	$123.70
Purchase #5	$113.64	6.194%	$120.6789	$120.68	$120.70	$120.70
Purchase #6	$208.46	3.168%	$215.064	$215.06	$215.05	$215.10
Purchase #7	$86.61	13.820%	$98.5795	$98.58	$98.60	$98.60
7 purchase totals =	$862.84		$929.4167	$929.41	$929.45	$929.50