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 $160.35   5.544%   $169.2398   $169.24   $169.25   $169.20  
  Purchase #2 $55.75   3.297%   $57.5881   $57.59   $57.60   $57.60  
  Purchase #3 $111.61   9.545%   $122.2632   $122.26   $122.25   $122.30  
  Purchase #4 $135.89   7.816%   $146.5112   $146.51   $146.50   $146.50  
  Purchase #5 $163.69   11.464%   $182.4554   $182.46   $182.45   $182.50  
  Purchase #6 $235.95   12.515%   $265.4791   $265.48   $265.50   $265.50  
  Purchase #7 $72.34   5.197%   $76.0995   $76.10   $76.10   $76.10  
  7 purchase totals = $935.58       $1,019.6363   $1,019.64   $1,019.65   $1,019.70