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 $247.66   5.717%   $261.8187   $261.82   $261.80   $261.80  
  Purchase #2 $119.50   6.587%   $127.3715   $127.37   $127.35   $127.40  
  Purchase #3 $218.41   12.733%   $246.2201   $246.22   $246.20   $246.20  
  Purchase #4 $208.77   13.623%   $237.2107   $237.21   $237.20   $237.20  
  Purchase #5 $101.25   6.376%   $107.7057   $107.71   $107.70   $107.70  
  Purchase #6 $248.45   12.682%   $279.9584   $279.96   $279.95   $280.00  
  Purchase #7 $11.54   5.269%   $12.148   $12.15   $12.15   $12.10  
  7 purchase totals = $1,155.58       $1,272.4331   $1,272.44   $1,272.35   $1,272.40