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 $215.71   8.266%   $233.5406   $233.54   $233.55   $233.50  
  Purchase #2 $182.51   11.301%   $203.1355   $203.14   $203.15   $203.10  
  Purchase #3 $57.59   13.318%   $65.2598   $65.26   $65.25   $65.30  
  Purchase #4 $233.61   10.565%   $258.2909   $258.29   $258.30   $258.30  
  Purchase #5 $205.53   3.501%   $212.7256   $212.73   $212.75   $212.70  
  Purchase #6 $93.59   12.383%   $105.1792   $105.18   $105.20   $105.20  
  Purchase #7 $175.36   9.688%   $192.3489   $192.35   $192.35   $192.30  
  7 purchase totals = $1,163.90       $1,270.4805   $1,270.49   $1,270.55   $1,270.40