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 $99.42   8.214%   $107.5864   $107.59   $107.60   $107.60  
  Purchase #2 $155.37   13.769%   $176.7629   $176.76   $176.75   $176.80  
  Purchase #3 $25.26   6.159%   $26.8158   $26.82   $26.80   $26.80  
  Purchase #4 $11.63   5.220%   $12.2371   $12.24   $12.25   $12.20  
  Purchase #5 $217.82   8.652%   $236.6658   $236.67   $236.65   $236.70  
  Purchase #6 $68.76   11.514%   $76.677   $76.68   $76.70   $76.70  
  Purchase #7 $153.57   10.161%   $169.1742   $169.17   $169.15   $169.20  
  7 purchase totals = $731.83       $805.9192   $805.93   $805.90   $806.00