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 $237.65   13.339%   $269.3501   $269.35   $269.35   $269.40  
  Purchase #2 $159.83   6.102%   $169.5828   $169.58   $169.60   $169.60  
  Purchase #3 $13.51   3.651%   $14.0033   $14.00   $14.00   $14.00  
  Purchase #4 $249.67   11.353%   $278.015   $278.02   $278.00   $278.00  
  Purchase #5 $124.94   7.606%   $134.4429   $134.44   $134.45   $134.40  
  Purchase #6 $58.96   7.874%   $63.6025   $63.60   $63.60   $63.60  
  Purchase #7 $75.51   9.262%   $82.5037   $82.50   $82.50   $82.50  
  7 purchase totals = $920.07       $1,011.5003   $1,011.49   $1,011.50   $1,011.50