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 $227.44   12.598%   $256.0929   $256.09   $256.10   $256.10  
  Purchase #2 $141.97   3.722%   $147.2541   $147.25   $147.25   $147.30  
  Purchase #3 $114.37   8.535%   $124.1315   $124.13   $124.15   $124.10  
  Purchase #4 $237.69   12.132%   $266.5266   $266.53   $266.55   $266.50  
  Purchase #5 $216.65   4.162%   $225.667   $225.67   $225.65   $225.70  
  Purchase #6 $5.26   5.508%   $5.5497   $5.55   $5.55   $5.50  
  Purchase #7 $161.95   5.723%   $171.2184   $171.22   $171.20   $171.20  
  7 purchase totals = $1,105.33       $1,196.4402   $1,196.44   $1,196.45   $1,196.40