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	$200.95	13.177%	$227.4292	$227.43	$227.45	$227.40
Purchase #2	$133.72	7.355%	$143.5551	$143.56	$143.55	$143.60
Purchase #3	$141.77	13.277%	$160.5928	$160.59	$160.60	$160.60
Purchase #4	$100.65	8.609%	$109.315	$109.32	$109.30	$109.30
Purchase #5	$130.43	4.189%	$135.8937	$135.89	$135.90	$135.90
Purchase #6	$124.55	9.203%	$136.0123	$136.01	$136.00	$136.00
Purchase #7	$78.47	10.700%	$86.8663	$86.87	$86.85	$86.90
7 purchase totals =	$910.54		$999.6644	$999.67	$999.65	$999.70