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 $235.41   13.668%   $267.5858   $267.59   $267.60   $267.60  
  Purchase #2 $58.81   5.584%   $62.094   $62.09   $62.10   $62.10  
  Purchase #3 $11.40   8.404%   $12.3581   $12.36   $12.35   $12.40  
  Purchase #4 $23.55   13.828%   $26.8065   $26.81   $26.80   $26.80  
  Purchase #5 $199.74   5.172%   $210.0706   $210.07   $210.05   $210.10  
  Purchase #6 $227.64   3.167%   $234.8494   $234.85   $234.85   $234.80  
  Purchase #7 $29.99   8.633%   $32.579   $32.58   $32.60   $32.60  
  7 purchase totals = $786.54       $846.3434   $846.35   $846.35   $846.40