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 $74.84   8.780%   $81.411   $81.41   $81.40   $81.40  
  Purchase #2 $176.53   13.669%   $200.6599   $200.66   $200.65   $200.70  
  Purchase #3 $194.51   11.660%   $217.1899   $217.19   $217.20   $217.20  
  Purchase #4 $250.97   11.520%   $279.8817   $279.88   $279.90   $279.90  
  Purchase #5 $147.55   13.604%   $167.6227   $167.62   $167.60   $167.60  
  Purchase #6 $226.44   13.611%   $257.2607   $257.26   $257.25   $257.30  
  Purchase #7 $239.85   10.841%   $265.8521   $265.85   $265.85   $265.90  
  7 purchase totals = $1,310.69       $1,469.8780   $1,469.87   $1,469.85   $1,470.00