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	$27.97	12.589%	$31.4911	$31.49	$31.50	$31.50
Purchase #2	$73.43	6.805%	$78.4269	$78.43	$78.45	$78.40
Purchase #3	$151.85	8.722%	$165.0944	$165.09	$165.10	$165.10
Purchase #4	$91.58	9.846%	$100.597	$100.60	$100.60	$100.60
Purchase #5	$60.93	4.334%	$63.5707	$63.57	$63.55	$63.60
Purchase #6	$86.71	9.709%	$95.1287	$95.13	$95.15	$95.10
Purchase #7	$154.80	7.426%	$166.2954	$166.30	$166.30	$166.30
7 purchase totals =	$647.27		$700.6042	$700.61	$700.65	$700.60