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 $85.39   12.161%   $95.7743   $95.77   $95.75   $95.80  
  Purchase #2 $25.30   8.520%   $27.4556   $27.46   $27.45   $27.50  
  Purchase #3 $190.50   4.862%   $199.7621   $199.76   $199.75   $199.80  
  Purchase #4 $88.34   5.797%   $93.4611   $93.46   $93.45   $93.50  
  Purchase #5 $101.29   13.643%   $115.109   $115.11   $115.10   $115.10  
  Purchase #6 $158.85   10.618%   $175.7167   $175.72   $175.70   $175.70  
  Purchase #7 $247.50   12.156%   $277.5861   $277.59   $277.60   $277.60  
  7 purchase totals = $897.17       $984.8649   $984.87   $984.80   $985.00