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 $224.84   13.223%   $254.5706   $254.57   $254.55   $254.60  
  Purchase #2 $155.58   12.271%   $174.6712   $174.67   $174.65   $174.70  
  Purchase #3 $33.55   5.212%   $35.2986   $35.30   $35.30   $35.30  
  Purchase #4 $177.42   12.531%   $199.6525   $199.65   $199.65   $199.70  
  Purchase #5 $62.80   6.259%   $66.7307   $66.73   $66.75   $66.70  
  Purchase #6 $61.32   13.220%   $69.4265   $69.43   $69.45   $69.40  
  Purchase #7 $220.55   3.640%   $228.578   $228.58   $228.60   $228.60  
  7 purchase totals = $936.06       $1,028.9281   $1,028.93   $1,028.95   $1,029.00