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 $58.38   6.321%   $62.0702   $62.07   $62.05   $62.10  
  Purchase #2 $74.45   13.102%   $84.2044   $84.20   $84.20   $84.20  
  Purchase #3 $15.82   8.121%   $17.1047   $17.10   $17.10   $17.10  
  Purchase #4 $236.92   10.282%   $261.2801   $261.28   $261.30   $261.30  
  Purchase #5 $54.77   13.588%   $62.2121   $62.21   $62.20   $62.20  
  Purchase #6 $250.87   11.629%   $280.0437   $280.04   $280.05   $280.00  
  Purchase #7 $172.82   12.698%   $194.7647   $194.76   $194.75   $194.80  
  7 purchase totals = $864.03       $961.6799   $961.66   $961.65   $961.70