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 $48.66   13.563%   $55.2598   $55.26   $55.25   $55.30  
  Purchase #2 $229.40   6.219%   $243.6664   $243.67   $243.65   $243.70  
  Purchase #3 $67.99   13.255%   $77.0021   $77.00   $77.00   $77.00  
  Purchase #4 $126.40   11.750%   $141.252   $141.25   $141.25   $141.30  
  Purchase #5 $122.80   8.416%   $133.1348   $133.13   $133.15   $133.10  
  Purchase #6 $68.92   13.809%   $78.4372   $78.44   $78.45   $78.40  
  Purchase #7 $70.71   8.710%   $76.8688   $76.87   $76.85   $76.90  
  7 purchase totals = $734.88       $805.6211   $805.62   $805.60   $805.70