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	$104.90	6.288%	$111.4961	$111.50	$111.50	$111.50
Purchase #2	$45.63	13.437%	$51.7613	$51.76	$51.75	$51.80
Purchase #3	$93.82	9.766%	$102.9825	$102.98	$103.00	$103.00
Purchase #4	$31.44	13.866%	$35.7995	$35.80	$35.80	$35.80
Purchase #5	$81.38	11.629%	$90.8437	$90.84	$90.85	$90.80
Purchase #6	$224.25	13.106%	$253.6402	$253.64	$253.65	$253.60
Purchase #7	$132.29	4.132%	$137.7562	$137.76	$137.75	$137.80
7 purchase totals =	$713.71		$784.2795	$784.28	$784.30	$784.30