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 $247.29   3.698%   $256.4348   $256.43   $256.45   $256.40  
  Purchase #2 $180.28   11.533%   $201.0717   $201.07   $201.05   $201.10  
  Purchase #3 $186.38   10.481%   $205.9145   $205.91   $205.90   $205.90  
  Purchase #4 $210.54   13.863%   $239.7272   $239.73   $239.75   $239.70  
  Purchase #5 $246.39   8.325%   $266.902   $266.90   $266.90   $266.90  
  Purchase #6 $92.45   3.438%   $95.6284   $95.63   $95.65   $95.60  
  Purchase #7 $166.62   7.587%   $179.2615   $179.26   $179.25   $179.30  
  7 purchase totals = $1,329.95       $1,444.9401   $1,444.93   $1,444.95   $1,444.90