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	$100.47	13.277%	$113.8094	$113.81	$113.80	$113.80
Purchase #2	$95.65	8.277%	$103.567	$103.57	$103.55	$103.60
Purchase #3	$125.61	8.557%	$136.3584	$136.36	$136.35	$136.40
Purchase #4	$78.54	4.745%	$82.2667	$82.27	$82.25	$82.30
Purchase #5	$61.85	10.678%	$68.4543	$68.45	$68.45	$68.50
Purchase #6	$47.70	10.274%	$52.6007	$52.60	$52.60	$52.60
Purchase #7	$13.45	11.570%	$15.0062	$15.01	$15.00	$15.00
7 purchase totals =	$523.27		$572.0627	$572.07	$572.00	$572.20