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 $57.93   8.601%   $62.9126   $62.91   $62.90   $62.90  
  Purchase #2 $168.91   8.212%   $182.7809   $182.78   $182.80   $182.80  
  Purchase #3 $141.68   5.710%   $149.7699   $149.77   $149.75   $149.80  
  Purchase #4 $12.94   9.511%   $14.1707   $14.17   $14.15   $14.20  
  Purchase #5 $96.63   13.215%   $109.3997   $109.40   $109.40   $109.40  
  Purchase #6 $237.58   9.179%   $259.3875   $259.39   $259.40   $259.40  
  Purchase #7 $143.41   12.425%   $161.2287   $161.23   $161.25   $161.20  
  7 purchase totals = $859.08       $939.6500   $939.65   $939.65   $939.70