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 $104.57   11.150%   $116.2296   $116.23   $116.25   $116.20  
  Purchase #2 $192.76   6.754%   $205.779   $205.78   $205.80   $205.80  
  Purchase #3 $11.48   11.237%   $12.77   $12.77   $12.75   $12.80  
  Purchase #4 $158.32   12.214%   $177.6572   $177.66   $177.65   $177.70  
  Purchase #5 $168.82   10.710%   $186.9006   $186.90   $186.90   $186.90  
  Purchase #6 $184.92   12.732%   $208.464   $208.46   $208.45   $208.50  
  Purchase #7 $82.94   3.641%   $85.9598   $85.96   $85.95   $86.00  
  7 purchase totals = $903.81       $993.7602   $993.76   $993.75   $993.90