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 $217.25   8.606%   $235.9465   $235.95   $235.95   $235.90  
  Purchase #2 $208.36   11.602%   $232.5339   $232.53   $232.55   $232.50  
  Purchase #3 $73.85   3.264%   $76.2605   $76.26   $76.25   $76.30  
  Purchase #4 $92.93   13.586%   $105.5555   $105.56   $105.55   $105.60  
  Purchase #5 $203.85   4.232%   $212.4769   $212.48   $212.50   $212.50  
  Purchase #6 $111.91   6.280%   $118.9379   $118.94   $118.95   $118.90  
  Purchase #7 $230.34   11.451%   $256.7162   $256.72   $256.70   $256.70  
  7 purchase totals = $1,138.49       $1,238.4274   $1,238.44   $1,238.45   $1,238.40