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 $61.72   6.401%   $65.6707   $65.67   $65.65   $65.70  
  Purchase #2 $179.73   13.776%   $204.4896   $204.49   $204.50   $204.50  
  Purchase #3 $126.93   4.856%   $133.0937   $133.09   $133.10   $133.10  
  Purchase #4 $71.62   4.306%   $74.704   $74.70   $74.70   $74.70  
  Purchase #5 $133.97   4.287%   $139.7133   $139.71   $139.70   $139.70  
  Purchase #6 $104.58   11.605%   $116.7165   $116.72   $116.70   $116.70  
  Purchase #7 $42.92   13.626%   $48.7683   $48.77   $48.75   $48.80  
  7 purchase totals = $721.47       $783.1561   $783.15   $783.10   $783.20