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 $249.98   5.791%   $264.4563   $264.46   $264.45   $264.50  
  Purchase #2 $169.99   4.153%   $177.0497   $177.05   $177.05   $177.00  
  Purchase #3 $248.39   5.522%   $262.1061   $262.11   $262.10   $262.10  
  Purchase #4 $223.26   3.333%   $230.7013   $230.70   $230.70   $230.70  
  Purchase #5 $210.56   11.667%   $235.126   $235.13   $235.15   $235.10  
  Purchase #6 $73.26   3.143%   $75.5626   $75.56   $75.55   $75.60  
  Purchase #7 $111.25   8.524%   $120.733   $120.73   $120.75   $120.70  
  7 purchase totals = $1,286.69       $1,365.7350   $1,365.74   $1,365.75   $1,365.70