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 $172.32   11.688%   $192.4608   $192.46   $192.45   $192.50  
  Purchase #2 $221.56   11.329%   $246.6605   $246.66   $246.65   $246.70  
  Purchase #3 $5.26   12.726%   $5.9294   $5.93   $5.95   $5.90  
  Purchase #4 $217.34   5.393%   $229.0611   $229.06   $229.05   $229.10  
  Purchase #5 $86.75   9.672%   $95.1405   $95.14   $95.15   $95.10  
  Purchase #6 $250.79   3.545%   $259.6805   $259.68   $259.70   $259.70  
  Purchase #7 $158.25   8.707%   $172.0288   $172.03   $172.05   $172.00  
  7 purchase totals = $1,112.27       $1,200.9616   $1,200.96   $1,201.00   $1,201.00