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 $248.33   6.201%   $263.7289   $263.73   $263.75   $263.70  
  Purchase #2 $246.87   4.682%   $258.4285   $258.43   $258.45   $258.40  
  Purchase #3 $12.86   5.652%   $13.5868   $13.59   $13.60   $13.60  
  Purchase #4 $63.69   6.602%   $67.8948   $67.89   $67.90   $67.90  
  Purchase #5 $153.80   8.856%   $167.4205   $167.42   $167.40   $167.40  
  Purchase #6 $119.52   12.484%   $134.4409   $134.44   $134.45   $134.40  
  Purchase #7 $122.79   11.724%   $137.1859   $137.19   $137.20   $137.20  
  7 purchase totals = $967.86       $1,042.6863   $1,042.69   $1,042.75   $1,042.60