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	$72.92	7.553%	$78.4276	$78.43	$78.45	$78.40
Purchase #2	$70.98	9.712%	$77.8736	$77.87	$77.85	$77.90
Purchase #3	$49.79	13.424%	$56.4738	$56.47	$56.45	$56.50
Purchase #4	$187.90	11.667%	$209.8223	$209.82	$209.80	$209.80
Purchase #5	$145.96	13.787%	$166.0835	$166.08	$166.10	$166.10
Purchase #6	$93.89	10.580%	$103.8236	$103.82	$103.80	$103.80
Purchase #7	$205.45	10.778%	$227.5934	$227.59	$227.60	$227.60
7 purchase totals =	$826.89		$920.0978	$920.08	$920.05	$920.10