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 $55.79   12.312%   $62.6589   $62.66   $62.65   $62.70  
  Purchase #2 $212.89   6.534%   $226.8002   $226.80   $226.80   $226.80  
  Purchase #3 $15.45   13.318%   $17.5076   $17.51   $17.50   $17.50  
  Purchase #4 $82.65   4.380%   $86.2701   $86.27   $86.25   $86.30  
  Purchase #5 $179.33   7.673%   $193.09   $193.09   $193.10   $193.10  
  Purchase #6 $117.43   6.573%   $125.1487   $125.15   $125.15   $125.10  
  Purchase #7 $113.60   3.728%   $117.835   $117.84   $117.85   $117.80  
  7 purchase totals = $777.14       $829.3105   $829.32   $829.30   $829.30