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 $206.53   13.437%   $234.2814   $234.28   $234.30   $234.30  
  Purchase #2 $188.94   9.838%   $207.5279   $207.53   $207.55   $207.50  
  Purchase #3 $247.48   10.685%   $273.9232   $273.92   $273.90   $273.90  
  Purchase #4 $240.56   8.455%   $260.8993   $260.90   $260.90   $260.90  
  Purchase #5 $30.31   8.602%   $32.9173   $32.92   $32.90   $32.90  
  Purchase #6 $51.97   8.857%   $56.573   $56.57   $56.55   $56.60  
  Purchase #7 $16.89   9.408%   $18.479   $18.48   $18.50   $18.50  
  7 purchase totals = $982.68       $1,084.6011   $1,084.60   $1,084.60   $1,084.60