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	$55.82	13.448%	$63.3267	$63.33	$63.35	$63.30
Purchase #2	$70.53	11.628%	$78.7312	$78.73	$78.75	$78.70
Purchase #3	$108.67	13.623%	$123.4741	$123.47	$123.45	$123.50
Purchase #4	$164.60	4.400%	$171.8424	$171.84	$171.85	$171.80
Purchase #5	$222.55	5.303%	$234.3518	$234.35	$234.35	$234.40
Purchase #6	$114.50	12.602%	$128.9293	$128.93	$128.95	$128.90
Purchase #7	$126.90	4.163%	$132.1828	$132.18	$132.20	$132.20
7 purchase totals =	$863.57		$932.8383	$932.83	$932.90	$932.80