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 $160.55   13.410%   $182.0798   $182.08   $182.10   $182.10  
  Purchase #2 $163.44   12.493%   $183.8586   $183.86   $183.85   $183.90  
  Purchase #3 $81.77   12.124%   $91.6838   $91.68   $91.70   $91.70  
  Purchase #4 $178.59   13.562%   $202.8104   $202.81   $202.80   $202.80  
  Purchase #5 $64.58   9.562%   $70.7551   $70.76   $70.75   $70.80  
  Purchase #6 $219.54   13.252%   $248.6334   $248.63   $248.65   $248.60  
  Purchase #7 $165.34   13.127%   $187.0442   $187.04   $187.05   $187.00  
  7 purchase totals = $1,033.81       $1,166.8653   $1,166.86   $1,166.90   $1,166.90