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 $242.34   13.653%   $275.4267   $275.43   $275.45   $275.40  
  Purchase #2 $107.85   10.856%   $119.5582   $119.56   $119.55   $119.60  
  Purchase #3 $99.92   13.813%   $113.7219   $113.72   $113.70   $113.70  
  Purchase #4 $202.51   11.354%   $225.503   $225.50   $225.50   $225.50  
  Purchase #5 $10.53   13.476%   $11.949   $11.95   $11.95   $11.90  
  Purchase #6 $174.85   11.831%   $195.5365   $195.54   $195.55   $195.50  
  Purchase #7 $20.53   12.844%   $23.1669   $23.17   $23.15   $23.20  
  7 purchase totals = $858.53       $964.8622   $964.87   $964.85   $964.80