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 $195.51   4.299%   $203.915   $203.92   $203.90   $203.90  
  Purchase #2 $173.41   12.705%   $195.4417   $195.44   $195.45   $195.40  
  Purchase #3 $42.99   10.436%   $47.4764   $47.48   $47.50   $47.50  
  Purchase #4 $176.35   12.583%   $198.5401   $198.54   $198.55   $198.50  
  Purchase #5 $56.92   13.115%   $64.3851   $64.39   $64.40   $64.40  
  Purchase #6 $69.61   9.179%   $75.9995   $76.00   $76.00   $76.00  
  Purchase #7 $204.42   11.267%   $227.452   $227.45   $227.45   $227.50  
  7 purchase totals = $919.21       $1,013.2098   $1,013.22   $1,013.25   $1,013.20