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 $208.48   8.484%   $226.1674   $226.17   $226.15   $226.20  
  Purchase #2 $6.61   9.511%   $7.2387   $7.24   $7.25   $7.20  
  Purchase #3 $127.68   6.186%   $135.5783   $135.58   $135.60   $135.60  
  Purchase #4 $128.42   4.742%   $134.5097   $134.51   $134.50   $134.50  
  Purchase #5 $180.98   3.175%   $186.7261   $186.73   $186.75   $186.70  
  Purchase #6 $202.94   11.805%   $226.8971   $226.90   $226.90   $226.90  
  Purchase #7 $176.48   5.731%   $186.5941   $186.59   $186.60   $186.60  
  7 purchase totals = $1,031.59       $1,103.7114   $1,103.72   $1,103.75   $1,103.70