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 $248.78   5.165%   $261.6295   $261.63   $261.65   $261.60  
  Purchase #2 $53.63   4.169%   $55.8658   $55.87   $55.85   $55.90  
  Purchase #3 $158.92   9.647%   $174.251   $174.25   $174.25   $174.30  
  Purchase #4 $242.74   12.326%   $272.6601   $272.66   $272.65   $272.70  
  Purchase #5 $211.74   8.772%   $230.3138   $230.31   $230.30   $230.30  
  Purchase #6 $186.72   12.304%   $209.694   $209.69   $209.70   $209.70  
  Purchase #7 $162.75   8.184%   $176.0695   $176.07   $176.05   $176.10  
  7 purchase totals = $1,265.28       $1,380.4837   $1,380.48   $1,380.45   $1,380.60