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 $162.29   11.202%   $180.4697   $180.47   $180.45   $180.50  
  Purchase #2 $211.93   3.633%   $219.6294   $219.63   $219.65   $219.60  
  Purchase #3 $111.98   11.151%   $124.4669   $124.47   $124.45   $124.50  
  Purchase #4 $218.56   10.152%   $240.7482   $240.75   $240.75   $240.70  
  Purchase #5 $94.34   8.622%   $102.474   $102.47   $102.45   $102.50  
  Purchase #6 $248.56   11.824%   $277.9497   $277.95   $277.95   $277.90  
  Purchase #7 $229.66   13.630%   $260.9627   $260.96   $260.95   $261.00  
  7 purchase totals = $1,277.32       $1,406.7006   $1,406.70   $1,406.65   $1,406.70