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 $179.29   13.786%   $204.0069   $204.01   $204.00   $204.00  
  Purchase #2 $62.68   5.696%   $66.2503   $66.25   $66.25   $66.30  
  Purchase #3 $30.97   5.649%   $32.7195   $32.72   $32.70   $32.70  
  Purchase #4 $86.30   10.285%   $95.176   $95.18   $95.20   $95.20  
  Purchase #5 $30.28   8.104%   $32.7339   $32.73   $32.75   $32.70  
  Purchase #6 $69.51   12.450%   $78.164   $78.16   $78.15   $78.20  
  Purchase #7 $116.90   6.858%   $124.917   $124.92   $124.90   $124.90  
  7 purchase totals = $575.93       $633.9676   $633.97   $633.95   $634.00