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	$104.85	13.338%	$118.8349	$118.83	$118.85	$118.80
Purchase #2	$86.42	4.248%	$90.0911	$90.09	$90.10	$90.10
Purchase #3	$141.60	3.746%	$146.9043	$146.90	$146.90	$146.90
Purchase #4	$232.67	11.443%	$259.2944	$259.29	$259.30	$259.30
Purchase #5	$231.86	3.346%	$239.618	$239.62	$239.60	$239.60
Purchase #6	$71.53	12.625%	$80.5607	$80.56	$80.55	$80.60
Purchase #7	$25.87	12.662%	$29.1457	$29.15	$29.15	$29.10
7 purchase totals =	$894.80		$964.4491	$964.44	$964.45	$964.40