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 $237.89   5.387%   $250.7051   $250.71   $250.70   $250.70  
  Purchase #2 $243.86   7.226%   $261.4813   $261.48   $261.50   $261.50  
  Purchase #3 $53.45   13.530%   $60.6818   $60.68   $60.70   $60.70  
  Purchase #4 $244.63   11.162%   $271.9356   $271.94   $271.95   $271.90  
  Purchase #5 $219.80   6.535%   $234.1639   $234.16   $234.15   $234.20  
  Purchase #6 $228.44   11.166%   $253.9476   $253.95   $253.95   $253.90  
  Purchase #7 $56.62   4.277%   $59.0416   $59.04   $59.05   $59.00  
  7 purchase totals = $1,284.69       $1,391.9569   $1,391.96   $1,392.00   $1,391.90