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	$100.80	3.540%	$104.3683	$104.37	$104.35	$104.40
Purchase #2	$214.90	13.746%	$244.4402	$244.44	$244.45	$244.40
Purchase #3	$121.83	10.406%	$134.5076	$134.51	$134.50	$134.50
Purchase #4	$178.35	12.363%	$200.3994	$200.40	$200.40	$200.40
Purchase #5	$134.51	8.548%	$146.0079	$146.01	$146.00	$146.00
Purchase #6	$62.71	10.240%	$69.1315	$69.13	$69.15	$69.10
Purchase #7	$38.84	9.475%	$42.5201	$42.52	$42.50	$42.50
7 purchase totals =	$851.94		$941.3750	$941.38	$941.35	$941.30