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 $217.69   8.366%   $235.9019   $235.90   $235.90   $235.90  
  Purchase #2 $68.93   7.526%   $74.1177   $74.12   $74.10   $74.10  
  Purchase #3 $101.40   7.112%   $108.6116   $108.61   $108.60   $108.60  
  Purchase #4 $237.56   5.614%   $250.8966   $250.90   $250.90   $250.90  
  Purchase #5 $99.87   12.851%   $112.7043   $112.70   $112.70   $112.70  
  Purchase #6 $175.72   11.541%   $195.9998   $196.00   $196.00   $196.00  
  Purchase #7 $24.71   8.839%   $26.8941   $26.89   $26.90   $26.90  
  7 purchase totals = $925.88       $1,005.1260   $1,005.12   $1,005.10   $1,005.10