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 $249.44   10.461%   $275.5339   $275.53   $275.55   $275.50  
  Purchase #2 $42.35   4.484%   $44.249   $44.25   $44.25   $44.20  
  Purchase #3 $66.56   12.789%   $75.0724   $75.07   $75.05   $75.10  
  Purchase #4 $141.40   9.795%   $155.2501   $155.25   $155.25   $155.30  
  Purchase #5 $83.30   13.569%   $94.603   $94.60   $94.60   $94.60  
  Purchase #6 $173.60   11.368%   $193.3348   $193.33   $193.35   $193.30  
  Purchase #7 $215.28   10.434%   $237.7423   $237.74   $237.75   $237.70  
  7 purchase totals = $971.93       $1,075.7855   $1,075.77   $1,075.80   $1,075.70