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 $116.48   5.732%   $123.1566   $123.16   $123.15   $123.20  
  Purchase #2 $56.74   5.665%   $59.9543   $59.95   $59.95   $60.00  
  Purchase #3 $23.93   13.554%   $27.1735   $27.17   $27.15   $27.20  
  Purchase #4 $93.29   10.313%   $102.911   $102.91   $102.90   $102.90  
  Purchase #5 $216.80   3.447%   $224.2731   $224.27   $224.25   $224.30  
  Purchase #6 $14.34   13.117%   $16.221   $16.22   $16.20   $16.20  
  Purchase #7 $23.74   10.156%   $26.151   $26.15   $26.15   $26.20  
  7 purchase totals = $545.32       $579.8405   $579.83   $579.75   $580.00