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 $69.50   10.260%   $76.6307   $76.63   $76.65   $76.60  
  Purchase #2 $112.83   11.418%   $125.7129   $125.71   $125.70   $125.70  
  Purchase #3 $85.83   3.591%   $88.9122   $88.91   $88.90   $88.90  
  Purchase #4 $9.68   4.587%   $10.124   $10.12   $10.10   $10.10  
  Purchase #5 $245.33   10.625%   $271.3963   $271.40   $271.40   $271.40  
  Purchase #6 $241.55   13.682%   $274.5989   $274.60   $274.60   $274.60  
  Purchase #7 $239.32   4.474%   $250.0272   $250.03   $250.05   $250.00  
  7 purchase totals = $1,004.04       $1,097.4022   $1,097.40   $1,097.40   $1,097.30