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 $58.53   8.567%   $63.5443   $63.54   $63.55   $63.50  
  Purchase #2 $63.62   6.681%   $67.8705   $67.87   $67.85   $67.90  
  Purchase #3 $203.53   9.695%   $223.2622   $223.26   $223.25   $223.30  
  Purchase #4 $186.69   11.240%   $207.674   $207.67   $207.65   $207.70  
  Purchase #5 $114.43   11.770%   $127.8984   $127.90   $127.90   $127.90  
  Purchase #6 $46.47   5.220%   $48.8957   $48.90   $48.90   $48.90  
  Purchase #7 $135.76   5.277%   $142.9241   $142.92   $142.90   $142.90  
  7 purchase totals = $809.03       $882.0692   $882.06   $882.00   $882.10