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	$72.60	9.450%	$79.4607	$79.46	$79.45	$79.50
Purchase #2	$85.83	5.440%	$90.4992	$90.50	$90.50	$90.50
Purchase #3	$122.58	12.797%	$138.2666	$138.27	$138.25	$138.30
Purchase #4	$38.92	12.518%	$43.792	$43.79	$43.80	$43.80
Purchase #5	$249.71	9.102%	$272.4386	$272.44	$272.45	$272.40
Purchase #6	$174.40	6.371%	$185.511	$185.51	$185.50	$185.50
Purchase #7	$122.44	12.192%	$137.3679	$137.37	$137.35	$137.40
7 purchase totals =	$866.48		$947.3360	$947.34	$947.30	$947.40