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 $23.60   10.348%   $26.0421   $26.04   $26.05   $26.00  
  Purchase #2 $236.59   6.692%   $252.4226   $252.42   $252.40   $252.40  
  Purchase #3 $125.67   5.611%   $132.7213   $132.72   $132.70   $132.70  
  Purchase #4 $161.85   7.387%   $173.8059   $173.81   $173.80   $173.80  
  Purchase #5 $45.51   6.343%   $48.3967   $48.40   $48.40   $48.40  
  Purchase #6 $247.61   3.342%   $255.8851   $255.89   $255.90   $255.90  
  Purchase #7 $84.62   11.146%   $94.0517   $94.05   $94.05   $94.10  
  7 purchase totals = $925.45       $983.3254   $983.33   $983.30   $983.30