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 $250.71   4.472%   $261.9218   $261.92   $261.90   $261.90  
  Purchase #2 $218.55   13.329%   $247.6805   $247.68   $247.70   $247.70  
  Purchase #3 $58.70   4.226%   $61.1807   $61.18   $61.20   $61.20  
  Purchase #4 $242.29   11.592%   $270.3763   $270.38   $270.40   $270.40  
  Purchase #5 $176.37   3.568%   $182.6629   $182.66   $182.65   $182.70  
  Purchase #6 $165.41   3.867%   $171.8064   $171.81   $171.80   $171.80  
  Purchase #7 $165.84   5.279%   $174.5947   $174.59   $174.60   $174.60  
  7 purchase totals = $1,277.87       $1,370.2233   $1,370.22   $1,370.25   $1,370.30