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 $246.87   5.627%   $260.7614   $260.76   $260.75   $260.80  
  Purchase #2 $215.95   3.271%   $223.0137   $223.01   $223.00   $223.00  
  Purchase #3 $23.54   12.147%   $26.3994   $26.40   $26.40   $26.40  
  Purchase #4 $197.54   8.712%   $214.7497   $214.75   $214.75   $214.70  
  Purchase #5 $39.36   10.490%   $43.4889   $43.49   $43.50   $43.50  
  Purchase #6 $231.63   3.227%   $239.1047   $239.10   $239.10   $239.10  
  Purchase #7 $11.27   6.377%   $11.9887   $11.99   $12.00   $12.00  
  7 purchase totals = $966.16       $1,019.5065   $1,019.50   $1,019.50   $1,019.50