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 $185.80   11.410%   $206.9998   $207.00   $207.00   $207.00  
  Purchase #2 $179.28   5.215%   $188.6295   $188.63   $188.65   $188.60  
  Purchase #3 $142.46   6.366%   $151.529   $151.53   $151.55   $151.50  
  Purchase #4 $19.97   7.296%   $21.427   $21.43   $21.45   $21.40  
  Purchase #5 $125.45   13.723%   $142.6655   $142.67   $142.65   $142.70  
  Purchase #6 $23.99   10.705%   $26.5581   $26.56   $26.55   $26.60  
  Purchase #7 $23.27   12.582%   $26.1978   $26.20   $26.20   $26.20  
  7 purchase totals = $700.22       $764.0067   $764.02   $764.05   $764.00