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 $214.65   13.117%   $242.8056   $242.81   $242.80   $242.80  
  Purchase #2 $171.89   8.189%   $185.9661   $185.97   $185.95   $186.00  
  Purchase #3 $6.29   5.306%   $6.6237   $6.62   $6.60   $6.60  
  Purchase #4 $236.35   4.533%   $247.0637   $247.06   $247.05   $247.10  
  Purchase #5 $26.84   10.692%   $29.7097   $29.71   $29.70   $29.70  
  Purchase #6 $119.62   4.198%   $124.6416   $124.64   $124.65   $124.60  
  Purchase #7 $230.86   13.169%   $261.262   $261.26   $261.25   $261.30  
  7 purchase totals = $1,006.50       $1,098.0724   $1,098.07   $1,098.00   $1,098.10