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 $69.42   9.760%   $76.1954   $76.20   $76.20   $76.20  
  Purchase #2 $237.81   4.546%   $248.6208   $248.62   $248.60   $248.60  
  Purchase #3 $56.29   12.508%   $63.3308   $63.33   $63.35   $63.30  
  Purchase #4 $58.92   6.132%   $62.533   $62.53   $62.55   $62.50  
  Purchase #5 $179.84   3.188%   $185.5733   $185.57   $185.55   $185.60  
  Purchase #6 $127.26   9.416%   $139.2428   $139.24   $139.25   $139.20  
  Purchase #7 $177.66   10.524%   $196.3569   $196.36   $196.35   $196.40  
  7 purchase totals = $907.20       $971.8530   $971.85   $971.85   $971.80