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	$135.95	6.271%	$144.4754	$144.48	$144.50	$144.50
Purchase #2	$123.87	11.359%	$137.9404	$137.94	$137.95	$137.90
Purchase #3	$50.63	10.273%	$55.8312	$55.83	$55.85	$55.80
Purchase #4	$6.26	11.776%	$6.9972	$7.00	$7.00	$7.00
Purchase #5	$187.61	4.190%	$195.4709	$195.47	$195.45	$195.50
Purchase #6	$159.42	13.461%	$180.8795	$180.88	$180.90	$180.90
Purchase #7	$155.42	5.615%	$164.1468	$164.15	$164.15	$164.10
7 purchase totals =	$819.16		$885.7414	$885.75	$885.80	$885.70