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	$19.57	10.313%	$21.5883	$21.59	$21.60	$21.60
Purchase #2	$76.43	12.540%	$86.0143	$86.01	$86.00	$86.00
Purchase #3	$17.35	13.130%	$19.6281	$19.63	$19.65	$19.60
Purchase #4	$63.93	3.257%	$66.0122	$66.01	$66.00	$66.00
Purchase #5	$225.45	13.720%	$256.3817	$256.38	$256.40	$256.40
Purchase #6	$91.34	10.111%	$100.5754	$100.58	$100.60	$100.60
Purchase #7	$218.36	11.548%	$243.5762	$243.58	$243.60	$243.60
7 purchase totals =	$712.43		$793.7762	$793.78	$793.85	$793.80