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 $46.41   5.656%   $49.0349   $49.03   $49.05   $49.00  
  Purchase #2 $240.83   8.524%   $261.3583   $261.36   $261.35   $261.40  
  Purchase #3 $247.99   5.571%   $261.8055   $261.81   $261.80   $261.80  
  Purchase #4 $168.75   6.861%   $180.3279   $180.33   $180.35   $180.30  
  Purchase #5 $72.63   6.289%   $77.1977   $77.20   $77.20   $77.20  
  Purchase #6 $94.50   10.619%   $104.535   $104.54   $104.55   $104.50  
  Purchase #7 $37.53   9.142%   $40.961   $40.96   $40.95   $41.00  
  7 purchase totals = $908.64       $975.2203   $975.23   $975.25   $975.20