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 $55.73   10.640%   $61.6597   $61.66   $61.65   $61.70  
  Purchase #2 $182.68   9.224%   $199.5304   $199.53   $199.55   $199.50  
  Purchase #3 $73.70   6.178%   $78.2532   $78.25   $78.25   $78.30  
  Purchase #4 $136.69   6.742%   $145.9056   $145.91   $145.90   $145.90  
  Purchase #5 $131.63   9.701%   $144.3994   $144.40   $144.40   $144.40  
  Purchase #6 $222.96   5.235%   $234.632   $234.63   $234.65   $234.60  
  Purchase #7 $87.95   10.494%   $97.1795   $97.18   $97.20   $97.20  
  7 purchase totals = $891.34       $961.5598   $961.56   $961.60   $961.60