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 $133.59   10.850%   $148.0845   $148.08   $148.10   $148.10  
  Purchase #2 $221.71   10.364%   $244.688   $244.69   $244.70   $244.70  
  Purchase #3 $239.52   4.624%   $250.5954   $250.60   $250.60   $250.60  
  Purchase #4 $200.59   7.151%   $214.9342   $214.93   $214.95   $214.90  
  Purchase #5 $121.83   11.831%   $136.2437   $136.24   $136.25   $136.20  
  Purchase #6 $230.89   7.249%   $247.6272   $247.63   $247.65   $247.60  
  Purchase #7 $171.43   7.271%   $183.8947   $183.89   $183.90   $183.90  
  7 purchase totals = $1,319.56       $1,426.0677   $1,426.06   $1,426.15   $1,426.00