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 $203.90   12.870%   $230.1419   $230.14   $230.15   $230.10  
  Purchase #2 $26.85   8.625%   $29.1658   $29.17   $29.15   $29.20  
  Purchase #3 $205.78   8.691%   $223.6643   $223.66   $223.65   $223.70  
  Purchase #4 $19.39   10.554%   $21.4364   $21.44   $21.45   $21.40  
  Purchase #5 $24.45   5.797%   $25.8674   $25.87   $25.85   $25.90  
  Purchase #6 $83.84   12.810%   $94.5799   $94.58   $94.60   $94.60  
  Purchase #7 $87.86   5.792%   $92.9489   $92.95   $92.95   $92.90  
  7 purchase totals = $652.07       $717.8046   $717.81   $717.80   $717.80