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 $28.27   13.421%   $32.0641   $32.06   $32.05   $32.10  
  Purchase #2 $136.62   5.585%   $144.2502   $144.25   $144.25   $144.30  
  Purchase #3 $9.48   4.622%   $9.9182   $9.92   $9.90   $9.90  
  Purchase #4 $176.68   11.281%   $196.6113   $196.61   $196.60   $196.60  
  Purchase #5 $177.81   8.312%   $192.5896   $192.59   $192.60   $192.60  
  Purchase #6 $107.45   5.554%   $113.4178   $113.42   $113.40   $113.40  
  Purchase #7 $70.39   7.515%   $75.6798   $75.68   $75.70   $75.70  
  7 purchase totals = $706.70       $764.5310   $764.53   $764.50   $764.60