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 $119.37   12.477%   $134.2638   $134.26   $134.25   $134.30  
  Purchase #2 $17.41   11.695%   $19.4461   $19.45   $19.45   $19.40  
  Purchase #3 $27.63   11.836%   $30.9003   $30.90   $30.90   $30.90  
  Purchase #4 $164.63   7.199%   $176.4817   $176.48   $176.50   $176.50  
  Purchase #5 $236.74   4.818%   $248.1461   $248.15   $248.15   $248.10  
  Purchase #6 $152.37   4.268%   $158.8732   $158.87   $158.85   $158.90  
  Purchase #7 $234.85   10.832%   $260.289   $260.29   $260.30   $260.30  
  7 purchase totals = $953.00       $1,028.4002   $1,028.40   $1,028.40   $1,028.40