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 $198.95   11.853%   $222.5315   $222.53   $222.55   $222.50  
  Purchase #2 $124.77   9.121%   $136.1503   $136.15   $136.15   $136.20  
  Purchase #3 $178.53   5.242%   $187.8885   $187.89   $187.90   $187.90  
  Purchase #4 $177.49   10.194%   $195.5833   $195.58   $195.60   $195.60  
  Purchase #5 $182.46   10.614%   $201.8263   $201.83   $201.85   $201.80  
  Purchase #6 $21.25   7.702%   $22.8867   $22.89   $22.90   $22.90  
  Purchase #7 $187.75   11.169%   $208.7198   $208.72   $208.70   $208.70  
  7 purchase totals = $1,071.20       $1,175.5864   $1,175.59   $1,175.65   $1,175.60