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	$21.44	9.455%	$23.4672	$23.47	$23.45	$23.50
Purchase #2	$143.29	8.662%	$155.7018	$155.70	$155.70	$155.70
Purchase #3	$12.83	4.223%	$13.3718	$13.37	$13.35	$13.40
Purchase #4	$182.75	7.426%	$196.321	$196.32	$196.30	$196.30
Purchase #5	$246.76	3.799%	$256.1344	$256.13	$256.15	$256.10
Purchase #6	$93.84	9.861%	$103.0936	$103.09	$103.10	$103.10
Purchase #7	$37.25	10.636%	$41.2119	$41.21	$41.20	$41.20
7 purchase totals =	$738.16		$789.3017	$789.29	$789.25	$789.30