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 $92.62   8.714%   $100.6909   $100.69   $100.70   $100.70  
  Purchase #2 $228.58   3.429%   $236.418   $236.42   $236.40   $236.40  
  Purchase #3 $178.70   10.825%   $198.0443   $198.04   $198.05   $198.00  
  Purchase #4 $215.88   9.584%   $236.5699   $236.57   $236.55   $236.60  
  Purchase #5 $134.69   7.544%   $144.851   $144.85   $144.85   $144.90  
  Purchase #6 $71.31   7.724%   $76.818   $76.82   $76.80   $76.80  
  Purchase #7 $246.50   9.374%   $269.6069   $269.61   $269.60   $269.60  
  7 purchase totals = $1,168.28       $1,262.9990   $1,263.00   $1,262.95   $1,263.00