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	$228.55	13.737%	$259.9459	$259.95	$259.95	$259.90
Purchase #2	$57.78	13.286%	$65.4567	$65.46	$65.45	$65.50
Purchase #3	$140.50	7.646%	$151.2426	$151.24	$151.25	$151.20
Purchase #4	$64.79	10.246%	$71.4284	$71.43	$71.45	$71.40
Purchase #5	$93.38	9.399%	$102.1568	$102.16	$102.15	$102.20
Purchase #6	$213.44	13.545%	$242.3504	$242.35	$242.35	$242.40
Purchase #7	$71.92	8.294%	$77.885	$77.89	$77.90	$77.90
7 purchase totals =	$870.36		$970.4658	$970.48	$970.50	$970.50