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 $234.86   13.837%   $267.3576   $267.36   $267.35   $267.40  
  Purchase #2 $133.79   11.197%   $148.7705   $148.77   $148.75   $148.80  
  Purchase #3 $129.56   3.709%   $134.3654   $134.37   $134.35   $134.40  
  Purchase #4 $84.51   10.259%   $93.1799   $93.18   $93.20   $93.20  
  Purchase #5 $116.85   8.339%   $126.5941   $126.59   $126.60   $126.60  
  Purchase #6 $92.57   5.278%   $97.4558   $97.46   $97.45   $97.50  
  Purchase #7 $78.79   4.724%   $82.512   $82.51   $82.50   $82.50  
  7 purchase totals = $870.93       $950.2353   $950.24   $950.20   $950.40