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 $201.93   11.361%   $224.8713   $224.87   $224.85   $224.90  
  Purchase #2 $239.57   3.262%   $247.3848   $247.38   $247.40   $247.40  
  Purchase #3 $165.73   6.797%   $176.9947   $176.99   $177.00   $177.00  
  Purchase #4 $37.44   8.441%   $40.6003   $40.60   $40.60   $40.60  
  Purchase #5 $30.69   5.525%   $32.3856   $32.39   $32.40   $32.40  
  Purchase #6 $69.35   13.257%   $78.5437   $78.54   $78.55   $78.50  
  Purchase #7 $202.32   11.451%   $225.4877   $225.49   $225.50   $225.50  
  7 purchase totals = $947.03       $1,026.2681   $1,026.26   $1,026.30   $1,026.30