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 $208.54   10.239%   $229.8924   $229.89   $229.90   $229.90  
  Purchase #2 $62.61   9.771%   $68.7276   $68.73   $68.75   $68.70  
  Purchase #3 $109.99   10.724%   $121.7853   $121.79   $121.80   $121.80  
  Purchase #4 $97.61   12.872%   $110.1744   $110.17   $110.15   $110.20  
  Purchase #5 $99.46   8.358%   $107.7729   $107.77   $107.75   $107.80  
  Purchase #6 $199.74   3.703%   $207.1364   $207.14   $207.15   $207.10  
  Purchase #7 $161.99   10.451%   $178.9196   $178.92   $178.90   $178.90  
  7 purchase totals = $939.94       $1,024.4086   $1,024.41   $1,024.40   $1,024.40