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 $59.75   9.757%   $65.5798   $65.58   $65.60   $65.60  
  Purchase #2 $68.96   4.503%   $72.0653   $72.07   $72.05   $72.10  
  Purchase #3 $199.28   9.349%   $217.9107   $217.91   $217.90   $217.90  
  Purchase #4 $86.39   6.724%   $92.1989   $92.20   $92.20   $92.20  
  Purchase #5 $43.93   6.189%   $46.6488   $46.65   $46.65   $46.60  
  Purchase #6 $98.55   11.831%   $110.2095   $110.21   $110.20   $110.20  
  Purchase #7 $22.28   10.662%   $24.6555   $24.66   $24.65   $24.70  
  7 purchase totals = $579.14       $629.2685   $629.28   $629.25   $629.30