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 $226.71   9.773%   $248.8664   $248.87   $248.85   $248.90  
  Purchase #2 $208.96   3.222%   $215.6927   $215.69   $215.70   $215.70  
  Purchase #3 $25.29   6.158%   $26.8474   $26.85   $26.85   $26.80  
  Purchase #4 $195.78   6.551%   $208.6055   $208.61   $208.60   $208.60  
  Purchase #5 $31.74   13.582%   $36.0509   $36.05   $36.05   $36.10  
  Purchase #6 $114.62   9.421%   $125.4184   $125.42   $125.40   $125.40  
  Purchase #7 $61.55   9.242%   $67.2385   $67.24   $67.25   $67.20  
  7 purchase totals = $864.65       $928.7198   $928.73   $928.70   $928.70