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	$42.94	4.423%	$44.8392	$44.84	$44.85	$44.80
Purchase #2	$160.70	13.818%	$182.9055	$182.91	$182.90	$182.90
Purchase #3	$95.47	8.546%	$103.6289	$103.63	$103.65	$103.60
Purchase #4	$72.53	7.559%	$78.0125	$78.01	$78.00	$78.00
Purchase #5	$104.98	4.793%	$110.0117	$110.01	$110.00	$110.00
Purchase #6	$28.50	10.850%	$31.5923	$31.59	$31.60	$31.60
Purchase #7	$125.45	4.833%	$131.513	$131.51	$131.50	$131.50
7 purchase totals =	$630.57		$682.5031	$682.50	$682.50	$682.40