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 $212.50   11.374%   $236.6698   $236.67   $236.65   $236.70  
  Purchase #2 $248.63   5.278%   $261.7527   $261.75   $261.75   $261.80  
  Purchase #3 $162.54   11.541%   $181.2987   $181.30   $181.30   $181.30  
  Purchase #4 $58.77   8.404%   $63.709   $63.71   $63.70   $63.70  
  Purchase #5 $217.95   4.719%   $228.2351   $228.24   $228.25   $228.20  
  Purchase #6 $237.58   9.577%   $260.333   $260.33   $260.35   $260.30  
  Purchase #7 $66.65   13.248%   $75.4798   $75.48   $75.50   $75.50  
  7 purchase totals = $1,204.62       $1,307.4781   $1,307.48   $1,307.50   $1,307.50