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 $60.94   10.223%   $67.1699   $67.17   $67.15   $67.20  
  Purchase #2 $246.98   8.605%   $268.2326   $268.23   $268.25   $268.20  
  Purchase #3 $245.42   6.854%   $262.2411   $262.24   $262.25   $262.20  
  Purchase #4 $167.59   13.635%   $190.4409   $190.44   $190.45   $190.40  
  Purchase #5 $235.68   12.744%   $265.7151   $265.72   $265.70   $265.70  
  Purchase #6 $127.94   9.492%   $140.0841   $140.08   $140.10   $140.10  
  Purchase #7 $71.92   6.786%   $76.8005   $76.80   $76.80   $76.80  
  7 purchase totals = $1,156.47       $1,270.6842   $1,270.68   $1,270.70   $1,270.60