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 $119.25   10.109%   $131.305   $131.31   $131.30   $131.30  
  Purchase #2 $239.57   9.343%   $261.953   $261.95   $261.95   $262.00  
  Purchase #3 $123.56   12.651%   $139.1916   $139.19   $139.20   $139.20  
  Purchase #4 $20.69   12.463%   $23.2686   $23.27   $23.25   $23.30  
  Purchase #5 $196.58   5.218%   $206.8375   $206.84   $206.85   $206.80  
  Purchase #6 $63.77   10.464%   $70.4429   $70.44   $70.45   $70.40  
  Purchase #7 $171.34   9.120%   $186.9662   $186.97   $186.95   $187.00  
  7 purchase totals = $934.76       $1,019.9648   $1,019.97   $1,019.95   $1,020.00