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 $233.68   13.246%   $264.6333   $264.63   $264.65   $264.60  
  Purchase #2 $63.31   5.481%   $66.78   $66.78   $66.80   $66.80  
  Purchase #3 $9.32   10.307%   $10.2806   $10.28   $10.30   $10.30  
  Purchase #4 $137.83   13.436%   $156.3488   $156.35   $156.35   $156.30  
  Purchase #5 $205.35   11.713%   $229.4026   $229.40   $229.40   $229.40  
  Purchase #6 $119.52   12.705%   $134.705   $134.71   $134.70   $134.70  
  Purchase #7 $239.38   12.724%   $269.8387   $269.84   $269.85   $269.80  
  7 purchase totals = $1,008.39       $1,131.9890   $1,131.99   $1,132.05   $1,131.90