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	$239.29	9.190%	$261.2808	$261.28	$261.30	$261.30
Purchase #2	$45.40	13.451%	$51.5068	$51.51	$51.50	$51.50
Purchase #3	$33.75	8.411%	$36.5887	$36.59	$36.60	$36.60
Purchase #4	$10.54	4.741%	$11.0397	$11.04	$11.05	$11.00
Purchase #5	$82.54	13.714%	$93.8595	$93.86	$93.85	$93.90
Purchase #6	$75.48	10.737%	$83.5843	$83.58	$83.60	$83.60
Purchase #7	$135.58	5.180%	$142.603	$142.60	$142.60	$142.60
7 purchase totals =	$622.58		$680.4628	$680.46	$680.50	$680.50