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 $61.77   7.708%   $66.5312   $66.53   $66.55   $66.50  
  Purchase #2 $169.81   8.161%   $183.6682   $183.67   $183.65   $183.70  
  Purchase #3 $179.31   4.157%   $186.7639   $186.76   $186.75   $186.80  
  Purchase #4 $196.54   4.643%   $205.6654   $205.67   $205.65   $205.70  
  Purchase #5 $160.25   4.770%   $167.8939   $167.89   $167.90   $167.90  
  Purchase #6 $78.92   9.841%   $86.6865   $86.69   $86.70   $86.70  
  Purchase #7 $249.68   3.131%   $257.4975   $257.50   $257.50   $257.50  
  7 purchase totals = $1,096.28       $1,154.7066   $1,154.71   $1,154.70   $1,154.80