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 $61.93   9.243%   $67.6542   $67.65   $67.65   $67.70  
  Purchase #2 $113.37   4.624%   $118.6122   $118.61   $118.60   $118.60  
  Purchase #3 $151.99   12.147%   $170.4522   $170.45   $170.45   $170.50  
  Purchase #4 $42.61   8.177%   $46.0942   $46.09   $46.10   $46.10  
  Purchase #5 $235.78   10.133%   $259.6716   $259.67   $259.65   $259.70  
  Purchase #6 $10.31   13.723%   $11.7248   $11.72   $11.70   $11.70  
  Purchase #7 $196.67   3.737%   $204.0196   $204.02   $204.00   $204.00  
  7 purchase totals = $812.66       $878.2288   $878.21   $878.15   $878.30