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 $78.76   5.338%   $82.9642   $82.96   $82.95   $83.00  
  Purchase #2 $146.99   11.358%   $163.6851   $163.69   $163.70   $163.70  
  Purchase #3 $30.83   10.587%   $34.094   $34.09   $34.10   $34.10  
  Purchase #4 $91.30   3.828%   $94.795   $94.80   $94.80   $94.80  
  Purchase #5 $84.44   12.691%   $95.1563   $95.16   $95.15   $95.20  
  Purchase #6 $178.34   6.224%   $189.4399   $189.44   $189.45   $189.40  
  Purchase #7 $89.47   9.119%   $97.6288   $97.63   $97.65   $97.60  
  7 purchase totals = $700.13       $757.7633   $757.77   $757.80   $757.80