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 $225.89   9.866%   $248.1763   $248.18   $248.20   $248.20  
  Purchase #2 $116.29   11.495%   $129.6575   $129.66   $129.65   $129.70  
  Purchase #3 $89.91   11.459%   $100.2128   $100.21   $100.20   $100.20  
  Purchase #4 $43.55   7.248%   $46.7065   $46.71   $46.70   $46.70  
  Purchase #5 $142.59   13.625%   $162.0179   $162.02   $162.00   $162.00  
  Purchase #6 $107.99   4.643%   $113.004   $113.00   $113.00   $113.00  
  Purchase #7 $223.66   5.725%   $236.4645   $236.46   $236.45   $236.50  
  7 purchase totals = $949.88       $1,036.2395   $1,036.24   $1,036.20   $1,036.30