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 $201.96   6.610%   $215.3096   $215.31   $215.30   $215.30  
  Purchase #2 $247.27   4.308%   $257.9224   $257.92   $257.90   $257.90  
  Purchase #3 $115.80   12.509%   $130.2854   $130.29   $130.30   $130.30  
  Purchase #4 $177.74   13.786%   $202.2432   $202.24   $202.25   $202.20  
  Purchase #5 $15.54   9.667%   $17.0423   $17.04   $17.05   $17.00  
  Purchase #6 $90.58   6.126%   $96.1289   $96.13   $96.15   $96.10  
  Purchase #7 $143.48   3.425%   $148.3942   $148.39   $148.40   $148.40  
  7 purchase totals = $992.37       $1,067.3260   $1,067.32   $1,067.35   $1,067.20