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 $208.57   8.673%   $226.6593   $226.66   $226.65   $226.70  
  Purchase #2 $244.38   9.187%   $266.8312   $266.83   $266.85   $266.80  
  Purchase #3 $217.77   13.676%   $247.5522   $247.55   $247.55   $247.60  
  Purchase #4 $156.43   4.453%   $163.3958   $163.40   $163.40   $163.40  
  Purchase #5 $71.90   9.153%   $78.481   $78.48   $78.50   $78.50  
  Purchase #6 $44.38   9.422%   $48.5615   $48.56   $48.55   $48.60  
  Purchase #7 $23.28   11.464%   $25.9488   $25.95   $25.95   $25.90  
  7 purchase totals = $966.71       $1,057.4298   $1,057.43   $1,057.45   $1,057.50