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 $65.49   8.553%   $71.0914   $71.09   $71.10   $71.10  
  Purchase #2 $248.37   5.854%   $262.9096   $262.91   $262.90   $262.90  
  Purchase #3 $78.60   12.538%   $88.4549   $88.45   $88.45   $88.50  
  Purchase #4 $28.85   5.492%   $30.4344   $30.43   $30.45   $30.40  
  Purchase #5 $193.57   6.781%   $206.696   $206.70   $206.70   $206.70  
  Purchase #6 $101.36   4.472%   $105.8928   $105.89   $105.90   $105.90  
  Purchase #7 $40.43   3.162%   $41.7084   $41.71   $41.70   $41.70  
  7 purchase totals = $756.67       $807.1875   $807.18   $807.20   $807.20