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 $24.58   7.856%   $26.511   $26.51   $26.50   $26.50  
  Purchase #2 $180.94   13.641%   $205.622   $205.62   $205.60   $205.60  
  Purchase #3 $68.64   9.620%   $75.2432   $75.24   $75.25   $75.20  
  Purchase #4 $197.25   10.743%   $218.4406   $218.44   $218.45   $218.40  
  Purchase #5 $175.87   11.584%   $196.2428   $196.24   $196.25   $196.20  
  Purchase #6 $125.98   11.148%   $140.0243   $140.02   $140.00   $140.00  
  Purchase #7 $197.66   6.277%   $210.0671   $210.07   $210.05   $210.10  
  7 purchase totals = $970.92       $1,072.1510   $1,072.14   $1,072.10   $1,072.00