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 $248.96   8.427%   $269.9399   $269.94   $269.95   $269.90  
  Purchase #2 $116.79   7.296%   $125.311   $125.31   $125.30   $125.30  
  Purchase #3 $106.38   7.752%   $114.6266   $114.63   $114.65   $114.60  
  Purchase #4 $213.29   8.637%   $231.7119   $231.71   $231.70   $231.70  
  Purchase #5 $65.44   7.605%   $70.4167   $70.42   $70.40   $70.40  
  Purchase #6 $122.46   11.510%   $136.5551   $136.56   $136.55   $136.60  
  Purchase #7 $87.73   12.135%   $98.376   $98.38   $98.40   $98.40  
  7 purchase totals = $961.05       $1,046.9372   $1,046.95   $1,046.95   $1,046.90