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 $157.94   12.757%   $178.0884   $178.09   $178.10   $178.10  
  Purchase #2 $22.59   5.382%   $23.8058   $23.81   $23.80   $23.80  
  Purchase #3 $248.63   6.773%   $265.4697   $265.47   $265.45   $265.50  
  Purchase #4 $217.93   11.309%   $242.5757   $242.58   $242.60   $242.60  
  Purchase #5 $95.79   11.448%   $106.756   $106.76   $106.75   $106.80  
  Purchase #6 $232.95   4.599%   $243.6634   $243.66   $243.65   $243.70  
  Purchase #7 $40.25   11.814%   $45.0051   $45.01   $45.00   $45.00  
  7 purchase totals = $1,016.08       $1,105.3641   $1,105.38   $1,105.35   $1,105.50