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	$226.27	11.156%	$251.5127	$251.51	$251.50	$251.50
Purchase #2	$150.29	7.720%	$161.8924	$161.89	$161.90	$161.90
Purchase #3	$180.68	10.829%	$200.2458	$200.25	$200.25	$200.20
Purchase #4	$87.83	7.566%	$94.4752	$94.48	$94.50	$94.50
Purchase #5	$92.87	11.483%	$103.5343	$103.53	$103.55	$103.50
Purchase #6	$73.96	5.566%	$78.0766	$78.08	$78.10	$78.10
Purchase #7	$100.85	8.726%	$109.6502	$109.65	$109.65	$109.70
7 purchase totals =	$912.75		$999.3872	$999.39	$999.45	$999.40