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 $84.53   13.424%   $95.8773   $95.88   $95.90   $95.90  
  Purchase #2 $60.28   11.801%   $67.3936   $67.39   $67.40   $67.40  
  Purchase #3 $243.36   5.827%   $257.5406   $257.54   $257.55   $257.50  
  Purchase #4 $179.78   12.873%   $202.9231   $202.92   $202.90   $202.90  
  Purchase #5 $130.66   7.677%   $140.6908   $140.69   $140.70   $140.70  
  Purchase #6 $169.95   11.624%   $189.705   $189.71   $189.70   $189.70  
  Purchase #7 $13.83   3.775%   $14.3521   $14.35   $14.35   $14.40  
  7 purchase totals = $882.39       $968.4825   $968.48   $968.50   $968.50