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 $24.54   7.785%   $26.4504   $26.45   $26.45   $26.50  
  Purchase #2 $74.25   3.118%   $76.5651   $76.57   $76.55   $76.60  
  Purchase #3 $119.89   10.760%   $132.7902   $132.79   $132.80   $132.80  
  Purchase #4 $236.50   9.216%   $258.2958   $258.30   $258.30   $258.30  
  Purchase #5 $114.41   4.668%   $119.7507   $119.75   $119.75   $119.80  
  Purchase #6 $187.79   5.238%   $197.6264   $197.63   $197.65   $197.60  
  Purchase #7 $14.59   3.404%   $15.0866   $15.09   $15.10   $15.10  
  7 purchase totals = $771.97       $826.5652   $826.58   $826.60   $826.70