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 $60.53   6.705%   $64.5885   $64.59   $64.60   $64.60  
  Purchase #2 $232.82   9.527%   $255.0008   $255.00   $255.00   $255.00  
  Purchase #3 $186.53   11.185%   $207.3934   $207.39   $207.40   $207.40  
  Purchase #4 $89.25   3.583%   $92.4478   $92.45   $92.45   $92.40  
  Purchase #5 $50.38   12.155%   $56.5037   $56.50   $56.50   $56.50  
  Purchase #6 $224.87   3.134%   $231.9174   $231.92   $231.90   $231.90  
  Purchase #7 $49.25   13.181%   $55.7416   $55.74   $55.75   $55.70  
  7 purchase totals = $893.63       $963.5932   $963.59   $963.60   $963.50