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 $236.46   9.792%   $259.6142   $259.61   $259.60   $259.60  
  Purchase #2 $229.77   7.462%   $246.9154   $246.92   $246.90   $246.90  
  Purchase #3 $63.78   3.348%   $65.9154   $65.92   $65.90   $65.90  
  Purchase #4 $212.79   6.503%   $226.6277   $226.63   $226.65   $226.60  
  Purchase #5 $153.76   4.469%   $160.6315   $160.63   $160.65   $160.60  
  Purchase #6 $107.40   6.519%   $114.4014   $114.40   $114.40   $114.40  
  Purchase #7 $126.51   6.672%   $134.9507   $134.95   $134.95   $135.00  
  7 purchase totals = $1,130.47       $1,209.0563   $1,209.06   $1,209.05   $1,209.00