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 $148.94   5.595%   $157.2732   $157.27   $157.25   $157.30  
  Purchase #2 $30.75   9.354%   $33.6264   $33.63   $33.65   $33.60  
  Purchase #3 $146.83   10.155%   $161.7406   $161.74   $161.75   $161.70  
  Purchase #4 $64.65   11.465%   $72.0621   $72.06   $72.05   $72.10  
  Purchase #5 $164.95   6.666%   $175.9456   $175.95   $175.95   $175.90  
  Purchase #6 $205.41   4.835%   $215.3416   $215.34   $215.35   $215.30  
  Purchase #7 $222.64   9.104%   $242.9091   $242.91   $242.90   $242.90  
  7 purchase totals = $984.17       $1,058.8986   $1,058.90   $1,058.90   $1,058.80