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 $125.73   8.160%   $135.9896   $135.99   $136.00   $136.00  
  Purchase #2 $10.30   10.857%   $11.4183   $11.42   $11.40   $11.40  
  Purchase #3 $144.78   9.665%   $158.773   $158.77   $158.75   $158.80  
  Purchase #4 $45.72   11.289%   $50.8813   $50.88   $50.90   $50.90  
  Purchase #5 $60.75   4.711%   $63.6119   $63.61   $63.60   $63.60  
  Purchase #6 $81.25   5.725%   $85.9016   $85.90   $85.90   $85.90  
  Purchase #7 $55.95   5.855%   $59.2259   $59.23   $59.25   $59.20  
  7 purchase totals = $524.48       $565.8016   $565.80   $565.80   $565.80