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 $229.51   10.733%   $254.1433   $254.14   $254.15   $254.10  
  Purchase #2 $210.61   10.797%   $233.3496   $233.35   $233.35   $233.30  
  Purchase #3 $76.35   12.421%   $85.8334   $85.83   $85.85   $85.80  
  Purchase #4 $221.31   12.275%   $248.4758   $248.48   $248.50   $248.50  
  Purchase #5 $24.90   7.163%   $26.6836   $26.68   $26.70   $26.70  
  Purchase #6 $176.73   11.228%   $196.5732   $196.57   $196.55   $196.60  
  Purchase #7 $125.25   11.486%   $139.6362   $139.64   $139.65   $139.60  
  7 purchase totals = $1,064.66       $1,184.6951   $1,184.69   $1,184.75   $1,184.60