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 $245.48   12.836%   $276.9898   $276.99   $277.00   $277.00  
  Purchase #2 $154.53   7.440%   $166.027   $166.03   $166.05   $166.00  
  Purchase #3 $76.37   7.284%   $81.9328   $81.93   $81.95   $81.90  
  Purchase #4 $99.31   4.689%   $103.9666   $103.97   $103.95   $104.00  
  Purchase #5 $23.39   9.560%   $25.6261   $25.63   $25.65   $25.60  
  Purchase #6 $119.81   10.254%   $132.0953   $132.10   $132.10   $132.10  
  Purchase #7 $242.85   7.874%   $261.972   $261.97   $261.95   $262.00  
  7 purchase totals = $961.74       $1,048.6096   $1,048.62   $1,048.65   $1,048.60