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 $127.98   10.681%   $141.6495   $141.65   $141.65   $141.60  
  Purchase #2 $102.69   11.795%   $114.8023   $114.80   $114.80   $114.80  
  Purchase #3 $147.88   4.300%   $154.2388   $154.24   $154.25   $154.20  
  Purchase #4 $177.30   5.436%   $186.938   $186.94   $186.95   $186.90  
  Purchase #5 $53.76   13.317%   $60.9192   $60.92   $60.90   $60.90  
  Purchase #6 $115.38   9.414%   $126.2419   $126.24   $126.25   $126.20  
  Purchase #7 $25.61   6.210%   $27.2004   $27.20   $27.20   $27.20  
  7 purchase totals = $750.60       $811.9901   $811.99   $812.00   $811.80