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 $17.62   10.246%   $19.4253   $19.43   $19.45   $19.40  
  Purchase #2 $177.58   7.244%   $190.4439   $190.44   $190.45   $190.40  
  Purchase #3 $225.34   7.790%   $242.894   $242.89   $242.90   $242.90  
  Purchase #4 $81.47   3.144%   $84.0314   $84.03   $84.05   $84.00  
  Purchase #5 $51.34   13.626%   $58.3356   $58.34   $58.35   $58.30  
  Purchase #6 $171.83   11.450%   $191.5045   $191.50   $191.50   $191.50  
  Purchase #7 $205.49   4.619%   $214.9816   $214.98   $215.00   $215.00  
  7 purchase totals = $930.67       $1,001.6163   $1,001.61   $1,001.70   $1,001.50