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 $200.69   12.648%   $226.0733   $226.07   $226.05   $226.10  
  Purchase #2 $156.68   4.383%   $163.5473   $163.55   $163.55   $163.50  
  Purchase #3 $51.78   7.664%   $55.7484   $55.75   $55.75   $55.70  
  Purchase #4 $236.73   9.404%   $258.9921   $258.99   $259.00   $259.00  
  Purchase #5 $155.25   13.216%   $175.7678   $175.77   $175.75   $175.80  
  Purchase #6 $123.70   6.385%   $131.5982   $131.60   $131.60   $131.60  
  Purchase #7 $196.88   13.707%   $223.8663   $223.87   $223.85   $223.90  
  7 purchase totals = $1,121.71       $1,235.5934   $1,235.60   $1,235.55   $1,235.60