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 $96.63   6.601%   $103.0085   $103.01   $103.00   $103.00  
  Purchase #2 $47.78   13.249%   $54.1104   $54.11   $54.10   $54.10  
  Purchase #3 $73.32   13.827%   $83.458   $83.46   $83.45   $83.50  
  Purchase #4 $95.55   12.577%   $107.5673   $107.57   $107.55   $107.60  
  Purchase #5 $155.58   3.126%   $160.4434   $160.44   $160.45   $160.40  
  Purchase #6 $81.89   13.311%   $92.7904   $92.79   $92.80   $92.80  
  Purchase #7 $249.49   6.439%   $265.5547   $265.55   $265.55   $265.60  
  7 purchase totals = $800.24       $866.9327   $866.93   $866.90   $867.00