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 $59.93   8.517%   $65.0342   $65.03   $65.05   $65.00  
  Purchase #2 $83.35   12.204%   $93.522   $93.52   $93.50   $93.50  
  Purchase #3 $168.28   5.440%   $177.4344   $177.43   $177.45   $177.40  
  Purchase #4 $122.85   3.264%   $126.8598   $126.86   $126.85   $126.90  
  Purchase #5 $57.72   10.245%   $63.6334   $63.63   $63.65   $63.60  
  Purchase #6 $65.64   12.663%   $73.952   $73.95   $73.95   $74.00  
  Purchase #7 $150.80   4.837%   $158.0942   $158.09   $158.10   $158.10  
  7 purchase totals = $708.57       $758.5300   $758.51   $758.55   $758.50