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 $73.97   5.475%   $78.0199   $78.02   $78.00   $78.00  
  Purchase #2 $53.93   4.147%   $56.1665   $56.17   $56.15   $56.20  
  Purchase #3 $21.51   11.731%   $24.0333   $24.03   $24.05   $24.00  
  Purchase #4 $95.80   12.487%   $107.7625   $107.76   $107.75   $107.80  
  Purchase #5 $94.69   9.340%   $103.534   $103.53   $103.55   $103.50  
  Purchase #6 $229.92   13.613%   $261.219   $261.22   $261.20   $261.20  
  Purchase #7 $156.38   5.872%   $165.5626   $165.56   $165.55   $165.60  
  7 purchase totals = $726.20       $796.2978   $796.29   $796.25   $796.30