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 $247.82   5.338%   $261.0486   $261.05   $261.05   $261.00  
  Purchase #2 $239.34   4.477%   $250.0553   $250.06   $250.05   $250.10  
  Purchase #3 $19.26   3.478%   $19.9299   $19.93   $19.95   $19.90  
  Purchase #4 $200.31   3.702%   $207.7255   $207.73   $207.75   $207.70  
  Purchase #5 $57.39   3.788%   $59.5639   $59.56   $59.55   $59.60  
  Purchase #6 $250.37   3.249%   $258.5045   $258.50   $258.50   $258.50  
  Purchase #7 $146.85   4.835%   $153.9502   $153.95   $153.95   $154.00  
  7 purchase totals = $1,161.34       $1,210.7779   $1,210.78   $1,210.80   $1,210.80