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 $63.32   4.269%   $66.0231   $66.02   $66.00   $66.00  
  Purchase #2 $124.42   8.551%   $135.0592   $135.06   $135.05   $135.10  
  Purchase #3 $174.56   9.841%   $191.7384   $191.74   $191.75   $191.70  
  Purchase #4 $83.27   5.595%   $87.929   $87.93   $87.95   $87.90  
  Purchase #5 $199.41   11.470%   $222.2823   $222.28   $222.30   $222.30  
  Purchase #6 $103.61   11.396%   $115.4174   $115.42   $115.40   $115.40  
  Purchase #7 $44.93   8.433%   $48.7189   $48.72   $48.70   $48.70  
  7 purchase totals = $793.52       $867.1683   $867.17   $867.15   $867.10