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 $58.55   11.206%   $65.1111   $65.11   $65.10   $65.10  
  Purchase #2 $63.54   4.510%   $66.4057   $66.41   $66.40   $66.40  
  Purchase #3 $231.90   13.217%   $262.5502   $262.55   $262.55   $262.60  
  Purchase #4 $164.65   11.363%   $183.3592   $183.36   $183.35   $183.40  
  Purchase #5 $212.89   7.258%   $228.3416   $228.34   $228.35   $228.30  
  Purchase #6 $54.87   3.752%   $56.9287   $56.93   $56.95   $56.90  
  Purchase #7 $208.76   9.563%   $228.7237   $228.72   $228.70   $228.70  
  7 purchase totals = $995.16       $1,091.4202   $1,091.42   $1,091.40   $1,091.40