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	$38.71	10.585%	$42.8075	$42.81	$42.80	$42.80
Purchase #2	$205.81	10.570%	$227.5641	$227.56	$227.55	$227.60
Purchase #3	$166.49	4.838%	$174.5448	$174.54	$174.55	$174.50
Purchase #4	$48.89	6.187%	$51.9148	$51.91	$51.90	$51.90
Purchase #5	$137.58	12.157%	$154.3056	$154.31	$154.30	$154.30
Purchase #6	$77.88	11.179%	$86.5862	$86.59	$86.60	$86.60
Purchase #7	$38.99	5.357%	$41.0787	$41.08	$41.10	$41.10
7 purchase totals =	$714.35		$778.8017	$778.80	$778.80	$778.80