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	$54.65	3.390%	$56.5026	$56.50	$56.50	$56.50
Purchase #2	$191.67	13.389%	$217.3327	$217.33	$217.35	$217.30
Purchase #3	$55.52	7.646%	$59.7651	$59.77	$59.75	$59.80
Purchase #4	$166.28	12.117%	$186.4281	$186.43	$186.45	$186.40
Purchase #5	$63.89	4.285%	$66.6277	$66.63	$66.65	$66.60
Purchase #6	$122.38	5.271%	$128.8306	$128.83	$128.85	$128.80
Purchase #7	$168.57	11.806%	$188.4714	$188.47	$188.45	$188.50
7 purchase totals =	$822.96		$903.9582	$903.96	$904.00	$903.90