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 $65.87   3.689%   $68.2999   $68.30   $68.30   $68.30  
  Purchase #2 $228.81   5.507%   $241.4106   $241.41   $241.40   $241.40  
  Purchase #3 $53.95   12.855%   $60.8853   $60.89   $60.90   $60.90  
  Purchase #4 $240.63   8.697%   $261.5576   $261.56   $261.55   $261.60  
  Purchase #5 $19.33   12.721%   $21.789   $21.79   $21.80   $21.80  
  Purchase #6 $28.97   9.681%   $31.7746   $31.77   $31.75   $31.80  
  Purchase #7 $75.45   13.624%   $85.7293   $85.73   $85.75   $85.70  
  7 purchase totals = $713.01       $771.4463   $771.45   $771.45   $771.50