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 $61.79   6.104%   $65.5617   $65.56   $65.55   $65.60  
  Purchase #2 $136.79   8.508%   $148.4281   $148.43   $148.45   $148.40  
  Purchase #3 $108.51   11.724%   $121.2317   $121.23   $121.25   $121.20  
  Purchase #4 $234.86   4.848%   $246.246   $246.25   $246.25   $246.20  
  Purchase #5 $244.91   13.552%   $278.1002   $278.10   $278.10   $278.10  
  Purchase #6 $163.33   3.827%   $169.5806   $169.58   $169.60   $169.60  
  Purchase #7 $205.99   12.497%   $231.7326   $231.73   $231.75   $231.70  
  7 purchase totals = $1,156.18       $1,260.8809   $1,260.88   $1,260.95   $1,260.80