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 $33.53   6.116%   $35.5807   $35.58   $35.60   $35.60  
  Purchase #2 $244.58   3.583%   $253.3433   $253.34   $253.35   $253.30  
  Purchase #3 $54.40   7.670%   $58.5725   $58.57   $58.55   $58.60  
  Purchase #4 $154.45   10.863%   $171.2279   $171.23   $171.25   $171.20  
  Purchase #5 $30.56   10.504%   $33.77   $33.77   $33.75   $33.80  
  Purchase #6 $192.89   10.419%   $212.9872   $212.99   $213.00   $213.00  
  Purchase #7 $233.92   8.114%   $252.9003   $252.90   $252.90   $252.90  
  7 purchase totals = $944.33       $1,018.3819   $1,018.38   $1,018.40   $1,018.40