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 $53.80   12.682%   $60.6229   $60.62   $60.60   $60.60  
  Purchase #2 $97.70   4.697%   $102.289   $102.29   $102.30   $102.30  
  Purchase #3 $106.57   10.335%   $117.584   $117.58   $117.60   $117.60  
  Purchase #4 $69.67   11.506%   $77.6862   $77.69   $77.70   $77.70  
  Purchase #5 $56.48   3.567%   $58.4946   $58.49   $58.50   $58.50  
  Purchase #6 $5.90   9.274%   $6.4472   $6.45   $6.45   $6.40  
  Purchase #7 $231.25   9.757%   $253.8131   $253.81   $253.80   $253.80  
  7 purchase totals = $621.37       $676.9370   $676.93   $676.95   $676.90