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 $229.79   12.742%   $259.0698   $259.07   $259.05   $259.10  
  Purchase #2 $68.62   7.683%   $73.8921   $73.89   $73.90   $73.90  
  Purchase #3 $224.38   5.166%   $235.9715   $235.97   $235.95   $236.00  
  Purchase #4 $249.63   8.374%   $270.534   $270.53   $270.55   $270.50  
  Purchase #5 $112.70   8.639%   $122.4362   $122.44   $122.45   $122.40  
  Purchase #6 $6.59   6.420%   $7.0131   $7.01   $7.00   $7.00  
  Purchase #7 $205.31   10.481%   $226.8285   $226.83   $226.85   $226.80  
  7 purchase totals = $1,097.02       $1,195.7452   $1,195.74   $1,195.75   $1,195.70