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 $193.99   5.838%   $205.3151   $205.32   $205.30   $205.30  
  Purchase #2 $23.25   12.527%   $26.1625   $26.16   $26.15   $26.20  
  Purchase #3 $5.58   12.432%   $6.2737   $6.27   $6.25   $6.30  
  Purchase #4 $156.91   8.242%   $169.8425   $169.84   $169.85   $169.80  
  Purchase #5 $200.46   3.290%   $207.0551   $207.06   $207.05   $207.10  
  Purchase #6 $52.98   13.269%   $60.0099   $60.01   $60.00   $60.00  
  Purchase #7 $130.26   7.469%   $139.9891   $139.99   $140.00   $140.00  
  7 purchase totals = $763.43       $814.6479   $814.65   $814.60   $814.70