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 $32.34   10.807%   $35.835   $35.84   $35.85   $35.80  
  Purchase #2 $21.36   9.581%   $23.4065   $23.41   $23.40   $23.40  
  Purchase #3 $142.83   7.563%   $153.6322   $153.63   $153.65   $153.60  
  Purchase #4 $209.79   5.492%   $221.3117   $221.31   $221.30   $221.30  
  Purchase #5 $18.97   10.314%   $20.9266   $20.93   $20.95   $20.90  
  Purchase #6 $207.91   8.624%   $225.8402   $225.84   $225.85   $225.80  
  Purchase #7 $134.86   5.452%   $142.2126   $142.21   $142.20   $142.20  
  7 purchase totals = $768.06       $823.1648   $823.17   $823.20   $823.00