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 $32.42   5.681%   $34.2618   $34.26   $34.25   $34.30  
  Purchase #2 $70.53   8.108%   $76.2486   $76.25   $76.25   $76.20  
  Purchase #3 $231.99   5.167%   $243.9769   $243.98   $244.00   $244.00  
  Purchase #4 $137.94   12.191%   $154.7563   $154.76   $154.75   $154.80  
  Purchase #5 $106.90   7.162%   $114.5562   $114.56   $114.55   $114.60  
  Purchase #6 $152.83   6.489%   $162.7471   $162.75   $162.75   $162.70  
  Purchase #7 $184.64   8.464%   $200.2679   $200.27   $200.25   $200.30  
  7 purchase totals = $917.25       $986.8148   $986.83   $986.80   $986.90