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 $66.97   10.856%   $74.2403   $74.24   $74.25   $74.20  
  Purchase #2 $119.60   9.867%   $131.4009   $131.40   $131.40   $131.40  
  Purchase #3 $69.93   6.757%   $74.6552   $74.66   $74.65   $74.70  
  Purchase #4 $61.78   6.808%   $65.986   $65.99   $66.00   $66.00  
  Purchase #5 $28.31   8.789%   $30.7982   $30.80   $30.80   $30.80  
  Purchase #6 $234.66   10.813%   $260.0338   $260.03   $260.05   $260.00  
  Purchase #7 $124.68   9.104%   $136.0309   $136.03   $136.05   $136.00  
  7 purchase totals = $705.93       $773.1453   $773.15   $773.20   $773.10