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 $60.36   4.675%   $63.1818   $63.18   $63.20   $63.20  
  Purchase #2 $222.95   6.586%   $237.6335   $237.63   $237.65   $237.60  
  Purchase #3 $23.89   9.591%   $26.1813   $26.18   $26.20   $26.20  
  Purchase #4 $187.41   5.646%   $197.9912   $197.99   $198.00   $198.00  
  Purchase #5 $136.92   8.260%   $148.2296   $148.23   $148.25   $148.20  
  Purchase #6 $26.78   3.723%   $27.777   $27.78   $27.80   $27.80  
  Purchase #7 $190.70   5.147%   $200.5153   $200.52   $200.50   $200.50  
  7 purchase totals = $849.01       $901.5097   $901.51   $901.60   $901.50