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 $72.98   13.691%   $82.9717   $82.97   $82.95   $83.00  
  Purchase #2 $54.96   5.480%   $57.9718   $57.97   $57.95   $58.00  
  Purchase #3 $14.94   10.828%   $16.5577   $16.56   $16.55   $16.60  
  Purchase #4 $235.31   10.218%   $259.354   $259.35   $259.35   $259.40  
  Purchase #5 $68.59   11.103%   $76.2055   $76.21   $76.20   $76.20  
  Purchase #6 $238.53   4.227%   $248.6127   $248.61   $248.60   $248.60  
  Purchase #7 $136.53   13.677%   $155.2032   $155.20   $155.20   $155.20  
  7 purchase totals = $821.84       $896.8766   $896.87   $896.80   $897.00