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 $239.68   11.261%   $266.6704   $266.67   $266.65   $266.70  
  Purchase #2 $187.32   10.219%   $206.4622   $206.46   $206.45   $206.50  
  Purchase #3 $56.94   11.482%   $63.4779   $63.48   $63.50   $63.50  
  Purchase #4 $104.83   9.863%   $115.1694   $115.17   $115.15   $115.20  
  Purchase #5 $166.95   4.594%   $174.6197   $174.62   $174.60   $174.60  
  Purchase #6 $173.55   4.263%   $180.9484   $180.95   $180.95   $180.90  
  Purchase #7 $65.75   4.492%   $68.7035   $68.70   $68.70   $68.70  
  7 purchase totals = $995.02       $1,076.0515   $1,076.05   $1,076.00   $1,076.10