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 $111.85   11.282%   $124.4689   $124.47   $124.45   $124.50  
  Purchase #2 $249.35   10.659%   $275.9282   $275.93   $275.95   $275.90  
  Purchase #3 $176.79   5.867%   $187.1623   $187.16   $187.15   $187.20  
  Purchase #4 $179.65   8.218%   $194.4136   $194.41   $194.40   $194.40  
  Purchase #5 $122.81   11.691%   $137.1677   $137.17   $137.15   $137.20  
  Purchase #6 $243.92   4.235%   $254.25   $254.25   $254.25   $254.30  
  Purchase #7 $222.26   6.622%   $236.9781   $236.98   $237.00   $237.00  
  7 purchase totals = $1,306.63       $1,410.3688   $1,410.37   $1,410.35   $1,410.50