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 $55.41   3.333%   $57.2568   $57.26   $57.25   $57.30  
  Purchase #2 $225.39   6.277%   $239.5377   $239.54   $239.55   $239.50  
  Purchase #3 $62.54   4.368%   $65.2717   $65.27   $65.25   $65.30  
  Purchase #4 $80.92   13.751%   $92.0473   $92.05   $92.05   $92.00  
  Purchase #5 $113.75   9.239%   $124.2594   $124.26   $124.25   $124.30  
  Purchase #6 $176.64   9.624%   $193.6398   $193.64   $193.65   $193.60  
  Purchase #7 $161.99   4.326%   $168.9977   $169.00   $169.00   $169.00  
  7 purchase totals = $876.64       $941.0104   $941.02   $941.00   $941.00