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 $197.93   10.116%   $217.9526   $217.95   $217.95   $218.00  
  Purchase #2 $9.88   11.524%   $11.0186   $11.02   $11.00   $11.00  
  Purchase #3 $177.88   7.522%   $191.2601   $191.26   $191.25   $191.30  
  Purchase #4 $175.98   12.346%   $197.7065   $197.71   $197.70   $197.70  
  Purchase #5 $187.38   13.645%   $212.948   $212.95   $212.95   $212.90  
  Purchase #6 $130.87   8.281%   $141.7073   $141.71   $141.70   $141.70  
  Purchase #7 $205.31   13.495%   $233.0166   $233.02   $233.00   $233.00  
  7 purchase totals = $1,085.23       $1,205.6097   $1,205.62   $1,205.55   $1,205.60