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 $61.73   6.803%   $65.9295   $65.93   $65.95   $65.90  
  Purchase #2 $38.71   7.716%   $41.6969   $41.70   $41.70   $41.70  
  Purchase #3 $27.71   8.388%   $30.0343   $30.03   $30.05   $30.00  
  Purchase #4 $177.63   10.833%   $196.8727   $196.87   $196.85   $196.90  
  Purchase #5 $200.64   11.496%   $223.7056   $223.71   $223.70   $223.70  
  Purchase #6 $54.39   3.245%   $56.155   $56.16   $56.15   $56.20  
  Purchase #7 $137.81   12.152%   $154.5567   $154.56   $154.55   $154.60  
  7 purchase totals = $698.62       $768.9507   $768.96   $768.95   $769.00