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 $23.42   12.234%   $26.2852   $26.29   $26.30   $26.30  
  Purchase #2 $127.85   5.285%   $134.6069   $134.61   $134.60   $134.60  
  Purchase #3 $135.50   13.145%   $153.3115   $153.31   $153.30   $153.30  
  Purchase #4 $134.86   4.746%   $141.2605   $141.26   $141.25   $141.30  
  Purchase #5 $246.75   12.212%   $276.8831   $276.88   $276.90   $276.90  
  Purchase #6 $238.99   4.183%   $248.987   $248.99   $249.00   $249.00  
  Purchase #7 $34.57   8.680%   $37.5707   $37.57   $37.55   $37.60  
  7 purchase totals = $941.94       $1,018.9049   $1,018.91   $1,018.90   $1,019.00