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 $170.25   12.615%   $191.727   $191.73   $191.75   $191.70  
  Purchase #2 $26.66   12.733%   $30.0546   $30.05   $30.05   $30.10  
  Purchase #3 $214.70   10.136%   $236.462   $236.46   $236.45   $236.50  
  Purchase #4 $49.72   13.247%   $56.3064   $56.31   $56.30   $56.30  
  Purchase #5 $41.43   6.179%   $43.99   $43.99   $44.00   $44.00  
  Purchase #6 $165.96   13.587%   $188.509   $188.51   $188.50   $188.50  
  Purchase #7 $172.36   12.262%   $193.4948   $193.49   $193.50   $193.50  
  7 purchase totals = $841.08       $940.5438   $940.54   $940.55   $940.60