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 $211.93   8.387%   $229.7046   $229.70   $229.70   $229.70  
  Purchase #2 $56.74   13.682%   $64.5032   $64.50   $64.50   $64.50  
  Purchase #3 $77.43   3.662%   $80.2655   $80.27   $80.25   $80.30  
  Purchase #4 $141.82   6.677%   $151.2893   $151.29   $151.30   $151.30  
  Purchase #5 $154.93   10.215%   $170.7561   $170.76   $170.75   $170.80  
  Purchase #6 $15.63   10.309%   $17.2413   $17.24   $17.25   $17.20  
  Purchase #7 $207.99   12.108%   $233.1734   $233.17   $233.15   $233.20  
  7 purchase totals = $866.47       $946.9334   $946.93   $946.90   $947.00