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 $48.77   12.827%   $55.0257   $55.03   $55.05   $55.00  
  Purchase #2 $220.85   4.359%   $230.4769   $230.48   $230.50   $230.50  
  Purchase #3 $16.95   9.583%   $18.5743   $18.57   $18.55   $18.60  
  Purchase #4 $192.88   5.812%   $204.0902   $204.09   $204.10   $204.10  
  Purchase #5 $169.69   4.665%   $177.606   $177.61   $177.60   $177.60  
  Purchase #6 $214.35   10.290%   $236.4066   $236.41   $236.40   $236.40  
  Purchase #7 $143.63   12.730%   $161.9141   $161.91   $161.90   $161.90  
  7 purchase totals = $1,007.12       $1,084.0938   $1,084.10   $1,084.10   $1,084.10