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	$21.76	7.119%	$23.3091	$23.31	$23.30	$23.30
Purchase #2	$148.31	10.226%	$163.4762	$163.48	$163.50	$163.50
Purchase #3	$79.32	13.175%	$89.7704	$89.77	$89.75	$89.80
Purchase #4	$116.66	13.857%	$132.8256	$132.83	$132.85	$132.80
Purchase #5	$118.80	4.786%	$124.4858	$124.49	$124.50	$124.50
Purchase #6	$85.76	11.291%	$95.4432	$95.44	$95.45	$95.40
Purchase #7	$99.39	10.595%	$109.9204	$109.92	$109.90	$109.90
7 purchase totals =	$670.00		$739.2307	$739.24	$739.25	$739.20