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 $191.75   8.736%   $208.5013   $208.50   $208.50   $208.50  
  Purchase #2 $125.50   7.296%   $134.6565   $134.66   $134.65   $134.70  
  Purchase #3 $134.73   3.457%   $139.3876   $139.39   $139.40   $139.40  
  Purchase #4 $107.36   5.192%   $112.9341   $112.93   $112.95   $112.90  
  Purchase #5 $201.59   8.509%   $218.7433   $218.74   $218.75   $218.70  
  Purchase #6 $130.71   4.663%   $136.805   $136.81   $136.80   $136.80  
  Purchase #7 $62.39   7.759%   $67.2308   $67.23   $67.25   $67.20  
  7 purchase totals = $954.03       $1,018.2586   $1,018.26   $1,018.30   $1,018.20