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 $67.72   12.854%   $76.4247   $76.42   $76.40   $76.40  
  Purchase #2 $175.57   9.587%   $192.4019   $192.40   $192.40   $192.40  
  Purchase #3 $111.46   5.130%   $117.1779   $117.18   $117.20   $117.20  
  Purchase #4 $57.65   11.537%   $64.3011   $64.30   $64.30   $64.30  
  Purchase #5 $63.32   3.264%   $65.3868   $65.39   $65.40   $65.40  
  Purchase #6 $229.62   4.413%   $239.7531   $239.75   $239.75   $239.80  
  Purchase #7 $93.69   8.651%   $101.7951   $101.80   $101.80   $101.80  
  7 purchase totals = $799.03       $857.2406   $857.24   $857.25   $857.30