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	$171.38	10.219%	$188.8933	$188.89	$188.90	$188.90
Purchase #2	$227.64	5.212%	$239.5046	$239.50	$239.50	$239.50
Purchase #3	$148.94	4.504%	$155.6483	$155.65	$155.65	$155.60
Purchase #4	$29.29	7.585%	$31.5116	$31.51	$31.50	$31.50
Purchase #5	$10.34	11.271%	$11.5054	$11.51	$11.50	$11.50
Purchase #6	$143.51	4.660%	$150.1976	$150.20	$150.20	$150.20
Purchase #7	$146.55	9.394%	$160.3169	$160.32	$160.30	$160.30
7 purchase totals =	$877.65		$937.5777	$937.58	$937.55	$937.50