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 $200.91   10.762%   $222.5319   $222.53   $222.55   $222.50  
  Purchase #2 $37.39   3.626%   $38.7458   $38.75   $38.75   $38.70  
  Purchase #3 $220.26   9.629%   $241.4688   $241.47   $241.45   $241.50  
  Purchase #4 $195.57   10.219%   $215.5553   $215.56   $215.55   $215.60  
  Purchase #5 $123.89   8.411%   $134.3104   $134.31   $134.30   $134.30  
  Purchase #6 $98.63   13.793%   $112.234   $112.23   $112.25   $112.20  
  Purchase #7 $66.93   3.278%   $69.124   $69.12   $69.10   $69.10  
  7 purchase totals = $943.58       $1,033.9702   $1,033.97   $1,033.95   $1,033.90