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	$163.34	10.236%	$180.0595	$180.06	$180.05	$180.10
Purchase #2	$107.57	8.602%	$116.8232	$116.82	$116.80	$116.80
Purchase #3	$62.42	11.859%	$69.8224	$69.82	$69.80	$69.80
Purchase #4	$187.42	12.759%	$211.3329	$211.33	$211.35	$211.30
Purchase #5	$185.30	3.397%	$191.5946	$191.59	$191.60	$191.60
Purchase #6	$117.83	4.753%	$123.4305	$123.43	$123.45	$123.40
Purchase #7	$81.77	10.217%	$90.1244	$90.12	$90.10	$90.10
7 purchase totals =	$905.65		$983.1875	$983.17	$983.15	$983.10