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 $236.39   13.514%   $268.3357   $268.34   $268.35   $268.30  
  Purchase #2 $168.92   6.353%   $179.6515   $179.65   $179.65   $179.70  
  Purchase #3 $200.63   3.754%   $208.1617   $208.16   $208.15   $208.20  
  Purchase #4 $61.45   6.582%   $65.4946   $65.49   $65.50   $65.50  
  Purchase #5 $170.67   7.175%   $182.9156   $182.92   $182.90   $182.90  
  Purchase #6 $206.55   8.872%   $224.8751   $224.88   $224.90   $224.90  
  Purchase #7 $78.97   11.467%   $88.0255   $88.03   $88.05   $88.00  
  7 purchase totals = $1,123.58       $1,217.4597   $1,217.47   $1,217.50   $1,217.50