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	$61.30	9.127%	$66.8949	$66.89	$66.90	$66.90
Purchase #2	$160.92	12.291%	$180.6987	$180.70	$180.70	$180.70
Purchase #3	$83.72	6.491%	$89.1543	$89.15	$89.15	$89.20
Purchase #4	$227.52	6.121%	$241.4465	$241.45	$241.45	$241.40
Purchase #5	$170.84	4.706%	$178.8797	$178.88	$178.90	$178.90
Purchase #6	$182.69	12.583%	$205.6779	$205.68	$205.70	$205.70
Purchase #7	$8.32	3.299%	$8.5945	$8.59	$8.60	$8.60
7 purchase totals =	$895.31		$971.3465	$971.34	$971.40	$971.40