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 $212.27   5.521%   $223.9894   $223.99   $224.00   $224.00  
  Purchase #2 $59.97   9.432%   $65.6264   $65.63   $65.65   $65.60  
  Purchase #3 $11.89   9.226%   $12.987   $12.99   $13.00   $13.00  
  Purchase #4 $188.45   4.300%   $196.5534   $196.55   $196.55   $196.60  
  Purchase #5 $158.62   6.564%   $169.0318   $169.03   $169.05   $169.00  
  Purchase #6 $15.61   12.462%   $17.5553   $17.56   $17.55   $17.60  
  Purchase #7 $37.77   3.644%   $39.1463   $39.15   $39.15   $39.10  
  7 purchase totals = $684.58       $724.8896   $724.90   $724.95   $724.90