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 $108.77   13.859%   $123.8444   $123.84   $123.85   $123.80  
  Purchase #2 $109.53   4.108%   $114.0295   $114.03   $114.05   $114.00  
  Purchase #3 $55.25   12.126%   $61.9496   $61.95   $61.95   $61.90  
  Purchase #4 $175.38   10.165%   $193.2074   $193.21   $193.20   $193.20  
  Purchase #5 $153.36   11.276%   $170.6529   $170.65   $170.65   $170.70  
  Purchase #6 $177.87   4.724%   $186.2726   $186.27   $186.25   $186.30  
  Purchase #7 $170.31   4.529%   $178.0233   $178.02   $178.00   $178.00  
  7 purchase totals = $950.47       $1,027.9797   $1,027.97   $1,027.95   $1,027.90