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	$57.64	9.799%	$63.2881	$63.29	$63.30	$63.30
Purchase #2	$210.66	3.721%	$218.4987	$218.50	$218.50	$218.50
Purchase #3	$139.95	3.269%	$144.525	$144.53	$144.55	$144.50
Purchase #4	$112.44	9.806%	$123.4659	$123.47	$123.45	$123.50
Purchase #5	$51.44	6.855%	$54.9662	$54.97	$54.95	$55.00
Purchase #6	$29.89	10.682%	$33.0828	$33.08	$33.10	$33.10
Purchase #7	$244.32	10.501%	$269.976	$269.98	$270.00	$270.00
7 purchase totals =	$846.34		$907.8027	$907.82	$907.85	$907.90