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 $238.56   10.664%   $264   $264.00   $264.00   $264.00  
  Purchase #2 $65.65   5.513%   $69.2693   $69.27   $69.25   $69.30  
  Purchase #3 $85.97   4.770%   $90.0708   $90.07   $90.05   $90.10  
  Purchase #4 $179.79   13.515%   $204.0886   $204.09   $204.10   $204.10  
  Purchase #5 $85.75   9.151%   $93.597   $93.60   $93.60   $93.60  
  Purchase #6 $158.41   11.202%   $176.1551   $176.16   $176.15   $176.20  
  Purchase #7 $35.81   6.580%   $38.1663   $38.17   $38.15   $38.20  
  7 purchase totals = $849.94       $935.3471   $935.36   $935.30   $935.50