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	$130.65	13.666%	$148.5046	$148.50	$148.50	$148.50
Purchase #2	$49.76	12.329%	$55.8949	$55.89	$55.90	$55.90
Purchase #3	$158.33	13.548%	$179.7805	$179.78	$179.80	$179.80
Purchase #4	$81.68	10.758%	$90.4671	$90.47	$90.45	$90.50
Purchase #5	$57.54	9.584%	$63.0546	$63.05	$63.05	$63.10
Purchase #6	$59.81	3.464%	$61.8818	$61.88	$61.90	$61.90
Purchase #7	$223.50	7.125%	$239.4244	$239.42	$239.40	$239.40
7 purchase totals =	$761.27		$839.0079	$838.99	$839.00	$839.10