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 $92.95   8.853%   $101.1789   $101.18   $101.20   $101.20  
  Purchase #2 $236.94   10.542%   $261.9182   $261.92   $261.90   $261.90  
  Purchase #3 $79.77   4.748%   $83.5575   $83.56   $83.55   $83.60  
  Purchase #4 $23.97   8.675%   $26.0494   $26.05   $26.05   $26.00  
  Purchase #5 $70.41   12.536%   $79.2366   $79.24   $79.25   $79.20  
  Purchase #6 $217.61   11.425%   $242.4719   $242.47   $242.45   $242.50  
  Purchase #7 $169.33   6.677%   $180.6362   $180.64   $180.65   $180.60  
  7 purchase totals = $890.98       $975.0487   $975.06   $975.05   $975.00