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	$132.42	9.120%	$144.4967	$144.50	$144.50	$144.50
Purchase #2	$225.87	8.388%	$244.816	$244.82	$244.80	$244.80
Purchase #3	$37.69	11.232%	$41.9233	$41.92	$41.90	$41.90
Purchase #4	$137.86	9.792%	$151.3593	$151.36	$151.35	$151.40
Purchase #5	$166.68	8.631%	$181.0662	$181.07	$181.05	$181.10
Purchase #6	$148.91	9.330%	$162.8033	$162.80	$162.80	$162.80
Purchase #7	$53.59	3.725%	$55.5862	$55.59	$55.60	$55.60
7 purchase totals =	$903.02		$982.0510	$982.06	$982.00	$982.10