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 $208.37   12.744%   $234.9247   $234.92   $234.90   $234.90  
  Purchase #2 $167.65   13.775%   $190.7438   $190.74   $190.75   $190.70  
  Purchase #3 $17.39   13.291%   $19.7013   $19.70   $19.70   $19.70  
  Purchase #4 $227.77   7.719%   $245.3516   $245.35   $245.35   $245.40  
  Purchase #5 $239.67   4.792%   $251.155   $251.16   $251.15   $251.20  
  Purchase #6 $237.65   7.619%   $255.7566   $255.76   $255.75   $255.80  
  Purchase #7 $68.86   6.724%   $73.4901   $73.49   $73.50   $73.50  
  7 purchase totals = $1,167.36       $1,271.1231   $1,271.12   $1,271.10   $1,271.20