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 $28.90   4.115%   $30.0892   $30.09   $30.10   $30.10  
  Purchase #2 $184.71   8.260%   $199.967   $199.97   $199.95   $200.00  
  Purchase #3 $239.81   3.641%   $248.5415   $248.54   $248.55   $248.50  
  Purchase #4 $61.42   8.141%   $66.4202   $66.42   $66.40   $66.40  
  Purchase #5 $20.79   11.259%   $23.1307   $23.13   $23.15   $23.10  
  Purchase #6 $66.30   9.408%   $72.5375   $72.54   $72.55   $72.50  
  Purchase #7 $150.60   5.215%   $158.4538   $158.45   $158.45   $158.50  
  7 purchase totals = $752.53       $799.1399   $799.14   $799.15   $799.10