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 $61.74   5.693%   $65.2549   $65.25   $65.25   $65.30  
  Purchase #2 $196.44   5.406%   $207.0595   $207.06   $207.05   $207.10  
  Purchase #3 $242.78   8.856%   $264.2806   $264.28   $264.30   $264.30  
  Purchase #4 $147.88   13.278%   $167.5155   $167.52   $167.50   $167.50  
  Purchase #5 $234.56   11.384%   $261.2623   $261.26   $261.25   $261.30  
  Purchase #6 $168.81   5.288%   $177.7367   $177.74   $177.75   $177.70  
  Purchase #7 $211.59   11.305%   $235.5102   $235.51   $235.50   $235.50  
  7 purchase totals = $1,263.80       $1,378.6197   $1,378.62   $1,378.60   $1,378.70