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 $136.88   10.870%   $151.7589   $151.76   $151.75   $151.80  
  Purchase #2 $214.70   11.759%   $239.9466   $239.95   $239.95   $239.90  
  Purchase #3 $204.76   6.436%   $217.9384   $217.94   $217.95   $217.90  
  Purchase #4 $190.77   11.484%   $212.678   $212.68   $212.70   $212.70  
  Purchase #5 $241.76   8.358%   $261.9663   $261.97   $261.95   $262.00  
  Purchase #6 $142.42   10.667%   $157.6119   $157.61   $157.60   $157.60  
  Purchase #7 $89.82   6.829%   $95.9538   $95.95   $95.95   $96.00  
  7 purchase totals = $1,221.11       $1,337.8539   $1,337.86   $1,337.85   $1,337.90