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	$92.86	7.180%	$99.5273	$99.53	$99.55	$99.50
Purchase #2	$124.89	5.320%	$131.5341	$131.53	$131.55	$131.50
Purchase #3	$123.32	7.366%	$132.4038	$132.40	$132.40	$132.40
Purchase #4	$56.56	7.144%	$60.6006	$60.60	$60.60	$60.60
Purchase #5	$29.72	4.334%	$31.0081	$31.01	$31.00	$31.00
Purchase #6	$81.64	10.175%	$89.9469	$89.95	$89.95	$89.90
Purchase #7	$48.26	5.822%	$51.0697	$51.07	$51.05	$51.10
7 purchase totals =	$557.25		$596.0905	$596.09	$596.10	$596.00