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 $240.47   8.801%   $261.6338   $261.63   $261.65   $261.60  
  Purchase #2 $226.56   11.537%   $252.6982   $252.70   $252.70   $252.70  
  Purchase #3 $84.84   11.741%   $94.8011   $94.80   $94.80   $94.80  
  Purchase #4 $42.86   7.622%   $46.1268   $46.13   $46.15   $46.10  
  Purchase #5 $191.49   9.280%   $209.2603   $209.26   $209.25   $209.30  
  Purchase #6 $59.31   7.765%   $63.9154   $63.92   $63.90   $63.90  
  Purchase #7 $73.46   12.651%   $82.7534   $82.75   $82.75   $82.80  
  7 purchase totals = $918.99       $1,011.1890   $1,011.19   $1,011.20   $1,011.20