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 $211.94   7.221%   $227.2442   $227.24   $227.25   $227.20  
  Purchase #2 $60.41   12.247%   $67.8084   $67.81   $67.80   $67.80  
  Purchase #3 $248.85   11.136%   $276.5619   $276.56   $276.55   $276.60  
  Purchase #4 $228.47   13.166%   $258.5504   $258.55   $258.55   $258.60  
  Purchase #5 $69.66   13.660%   $79.1756   $79.18   $79.20   $79.20  
  Purchase #6 $132.79   8.610%   $144.2232   $144.22   $144.20   $144.20  
  Purchase #7 $184.62   6.373%   $196.3858   $196.39   $196.40   $196.40  
  7 purchase totals = $1,136.74       $1,249.9495   $1,249.95   $1,249.95   $1,250.00