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 $151.93   7.477%   $163.2898   $163.29   $163.30   $163.30  
  Purchase #2 $235.49   6.159%   $249.9938   $249.99   $250.00   $250.00  
  Purchase #3 $96.78   4.194%   $100.839   $100.84   $100.85   $100.80  
  Purchase #4 $185.66   7.406%   $199.41   $199.41   $199.40   $199.40  
  Purchase #5 $208.66   7.391%   $224.0821   $224.08   $224.10   $224.10  
  Purchase #6 $32.76   9.316%   $35.8119   $35.81   $35.80   $35.80  
  Purchase #7 $75.76   3.806%   $78.6434   $78.64   $78.65   $78.60  
  7 purchase totals = $987.04       $1,052.0700   $1,052.06   $1,052.10   $1,052.00