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 $241.29   6.489%   $256.9473   $256.95   $256.95   $256.90  
  Purchase #2 $32.73   13.697%   $37.213   $37.21   $37.20   $37.20  
  Purchase #3 $34.74   10.545%   $38.4033   $38.40   $38.40   $38.40  
  Purchase #4 $161.41   13.132%   $182.6064   $182.61   $182.60   $182.60  
  Purchase #5 $40.98   7.338%   $43.9871   $43.99   $44.00   $44.00  
  Purchase #6 $166.40   5.749%   $175.9663   $175.97   $175.95   $176.00  
  Purchase #7 $208.97   3.640%   $216.5765   $216.58   $216.60   $216.60  
  7 purchase totals = $886.52       $951.6999   $951.71   $951.70   $951.70