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 $23.53   8.523%   $25.5355   $25.54   $25.55   $25.50  
  Purchase #2 $27.43   10.379%   $30.277   $30.28   $30.30   $30.30  
  Purchase #3 $28.32   5.269%   $29.8122   $29.81   $29.80   $29.80  
  Purchase #4 $216.77   6.743%   $231.3868   $231.39   $231.40   $231.40  
  Purchase #5 $248.89   7.691%   $268.0321   $268.03   $268.05   $268.00  
  Purchase #6 $66.87   11.192%   $74.3541   $74.35   $74.35   $74.40  
  Purchase #7 $182.61   10.499%   $201.7822   $201.78   $201.80   $201.80  
  7 purchase totals = $794.42       $861.1799   $861.18   $861.25   $861.20