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 $203.67   13.794%   $231.7642   $231.76   $231.75   $231.80  
  Purchase #2 $68.76   11.841%   $76.9019   $76.90   $76.90   $76.90  
  Purchase #3 $200.76   3.688%   $208.164   $208.16   $208.15   $208.20  
  Purchase #4 $166.33   11.853%   $186.0451   $186.05   $186.05   $186.00  
  Purchase #5 $217.76   8.696%   $236.6964   $236.70   $236.70   $236.70  
  Purchase #6 $58.45   12.610%   $65.8205   $65.82   $65.80   $65.80  
  Purchase #7 $179.70   10.519%   $198.6026   $198.60   $198.60   $198.60  
  7 purchase totals = $1,095.43       $1,203.9947   $1,203.99   $1,203.95   $1,204.00