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 $38.79   12.697%   $43.7152   $43.72   $43.70   $43.70  
  Purchase #2 $181.36   11.203%   $201.6778   $201.68   $201.70   $201.70  
  Purchase #3 $234.75   11.293%   $261.2603   $261.26   $261.25   $261.30  
  Purchase #4 $71.72   4.141%   $74.6899   $74.69   $74.70   $74.70  
  Purchase #5 $74.43   11.593%   $83.0587   $83.06   $83.05   $83.10  
  Purchase #6 $16.51   7.192%   $17.6974   $17.70   $17.70   $17.70  
  Purchase #7 $89.57   7.185%   $96.0056   $96.01   $96.00   $96.00  
  7 purchase totals = $707.13       $778.1049   $778.12   $778.10   $778.20