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 $241.66   9.650%   $264.9802   $264.98   $265.00   $265.00  
  Purchase #2 $54.41   8.342%   $58.9489   $58.95   $58.95   $58.90  
  Purchase #3 $139.61   5.355%   $147.0861   $147.09   $147.10   $147.10  
  Purchase #4 $197.46   7.606%   $212.4788   $212.48   $212.50   $212.50  
  Purchase #5 $224.33   10.797%   $248.5509   $248.55   $248.55   $248.60  
  Purchase #6 $16.76   3.562%   $17.357   $17.36   $17.35   $17.40  
  Purchase #7 $166.62   3.481%   $172.42   $172.42   $172.40   $172.40  
  7 purchase totals = $1,040.85       $1,121.8219   $1,121.83   $1,121.85   $1,121.90