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 $217.58   11.321%   $242.2122   $242.21   $242.20   $242.20  
  Purchase #2 $98.38   9.436%   $107.6631   $107.66   $107.65   $107.70  
  Purchase #3 $64.62   7.614%   $69.5402   $69.54   $69.55   $69.50  
  Purchase #4 $177.59   7.492%   $190.895   $190.90   $190.90   $190.90  
  Purchase #5 $45.73   13.577%   $51.9388   $51.94   $51.95   $51.90  
  Purchase #6 $188.36   4.239%   $196.3446   $196.34   $196.35   $196.30  
  Purchase #7 $41.68   7.743%   $44.9073   $44.91   $44.90   $44.90  
  7 purchase totals = $833.94       $903.5012   $903.50   $903.50   $903.40