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 $202.30   3.136%   $208.6441   $208.64   $208.65   $208.60  
  Purchase #2 $77.98   4.743%   $81.6786   $81.68   $81.70   $81.70  
  Purchase #3 $36.76   10.399%   $40.5827   $40.58   $40.60   $40.60  
  Purchase #4 $119.96   6.234%   $127.4383   $127.44   $127.45   $127.40  
  Purchase #5 $221.25   12.357%   $248.5899   $248.59   $248.60   $248.60  
  Purchase #6 $242.42   11.516%   $270.3371   $270.34   $270.35   $270.30  
  Purchase #7 $212.35   10.863%   $235.4176   $235.42   $235.40   $235.40  
  7 purchase totals = $1,113.02       $1,212.6883   $1,212.69   $1,212.75   $1,212.60