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 $55.43   13.451%   $62.8859   $62.89   $62.90   $62.90  
  Purchase #2 $116.55   5.244%   $122.6619   $122.66   $122.65   $122.70  
  Purchase #3 $170.41   11.549%   $190.0907   $190.09   $190.10   $190.10  
  Purchase #4 $61.39   5.469%   $64.7474   $64.75   $64.75   $64.70  
  Purchase #5 $75.63   5.109%   $79.4939   $79.49   $79.50   $79.50  
  Purchase #6 $216.69   5.859%   $229.3859   $229.39   $229.40   $229.40  
  Purchase #7 $200.87   5.130%   $211.1746   $211.17   $211.15   $211.20  
  7 purchase totals = $896.97       $960.4403   $960.44   $960.45   $960.50