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 $34.69   11.352%   $38.628   $38.63   $38.65   $38.60  
  Purchase #2 $10.78   7.103%   $11.5457   $11.55   $11.55   $11.50  
  Purchase #3 $117.29   7.455%   $126.034   $126.03   $126.05   $126.00  
  Purchase #4 $206.98   12.191%   $232.2129   $232.21   $232.20   $232.20  
  Purchase #5 $176.92   11.210%   $196.7527   $196.75   $196.75   $196.80  
  Purchase #6 $109.88   6.525%   $117.0497   $117.05   $117.05   $117.00  
  Purchase #7 $134.32   7.773%   $144.7607   $144.76   $144.75   $144.80  
  7 purchase totals = $790.86       $866.9837   $866.98   $867.00   $866.90