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 $66.25   10.543%   $73.2347   $73.23   $73.25   $73.20  
  Purchase #2 $250.42   4.594%   $261.9243   $261.92   $261.90   $261.90  
  Purchase #3 $59.50   9.332%   $65.0525   $65.05   $65.05   $65.10  
  Purchase #4 $145.56   12.247%   $163.3867   $163.39   $163.40   $163.40  
  Purchase #5 $9.49   4.206%   $9.8891   $9.89   $9.90   $9.90  
  Purchase #6 $250.46   3.182%   $258.4296   $258.43   $258.45   $258.40  
  Purchase #7 $110.45   8.125%   $119.4241   $119.42   $119.40   $119.40  
  7 purchase totals = $892.13       $951.3410   $951.33   $951.35   $951.30