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 $230.59   11.856%   $257.9288   $257.93   $257.95   $257.90  
  Purchase #2 $165.96   5.262%   $174.6928   $174.69   $174.70   $174.70  
  Purchase #3 $236.63   11.208%   $263.1515   $263.15   $263.15   $263.20  
  Purchase #4 $64.28   11.456%   $71.6439   $71.64   $71.65   $71.60  
  Purchase #5 $40.41   9.324%   $44.1778   $44.18   $44.20   $44.20  
  Purchase #6 $97.92   3.393%   $101.2424   $101.24   $101.25   $101.20  
  Purchase #7 $111.47   5.102%   $117.1572   $117.16   $117.15   $117.20  
  7 purchase totals = $947.26       $1,029.9944   $1,029.99   $1,030.05   $1,030.00