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 $244.27   9.432%   $267.3095   $267.31   $267.30   $267.30  
  Purchase #2 $24.75   10.154%   $27.2631   $27.26   $27.25   $27.30  
  Purchase #3 $58.88   10.242%   $64.9105   $64.91   $64.90   $64.90  
  Purchase #4 $209.62   12.155%   $235.0993   $235.10   $235.10   $235.10  
  Purchase #5 $57.93   6.588%   $61.7464   $61.75   $61.75   $61.70  
  Purchase #6 $55.38   3.246%   $57.1776   $57.18   $57.20   $57.20  
  Purchase #7 $227.75   9.850%   $250.1834   $250.18   $250.20   $250.20  
  7 purchase totals = $878.58       $963.6898   $963.69   $963.70   $963.70